2012年7月22日星期日

Disney•Pixar - Partly Cloudy (2009) 720p

皮克斯出品，没什么要继续介绍的了

2012年6月8日星期五

看电影，《黄金大劫案》和《雷神托尔》

黄金大劫案

今天看了一下，挺有意思

在现在的国产片子里不算鹤立鸡群，但也算得上优秀

至于特效嘛，对于看惯了好莱坞效果的我们来说，说它很渣也只是种客观评价

日本军官鸟山 xxx 的表现可圈可点，比大部分日本片子里的日本人看起来有趣多了

严重的东北口音让我比较不适应，不过或许方言是导演喜欢的一种表达方式吧

他的每个片子都是地方口音很重的，比如《疯狂的石头》、《疯狂赛车》

话说，还好这次的片名不是叫《疯狂的金条》，不然我一定不看

雷神托尔

这片子也是今天看的

基本上是纯粹的爆米花电影，完全可以在半小时内看完并毫无遗憾

做出这个评价我是很可观的，因为我几乎没有跳地看完

不是因为好看，而是因为可以休息脑筋

关于看电影和休息

有人说看电影不算一种休息，因为看电影也很累很纠结，有时候看完会大笑或大哭，太刺激
有人说看电影纯粹是一种休息，每一部戏都是个扯淡，认真你就输了，再说看电影大笑大哭之后很放松，不用像过自己的人生那样戴面具

好吧，其实这两种说法，都是我说的

但是这次想说的是，看爆米花电影绝对是一种很好的休息

首先，通常来说电影的画面制作相对精良，看着不恶心。日剧、港剧神马的看起来就恶心了，韩国剧完全没法看，大陆片子质量相差太大，看起来有风险。美剧普遍是不错的，但有时候看美剧比爆米花电影费神得多，不适合休息

其次，如果真的什么也不看，发呆，或者听音乐，很容易陷入到思维的困境中，很累，更伤神

再次，看小说神马的就更累了——网络小说我不看，正经小说情节都太过跌宕

所以，我最喜欢的的保养头脑的方法，就是看爆米花电影

那么，那些是爆米花电影呢？

基本能从头看到尾，看完啥也没记住，只留下一两个画面的影片

1 不是很经典的老片子，别太挫就行

2 美国的所有英雄片

3 美国的所有体育、歌舞片

4 无厘头类的搞笑电影，比如 90 年代港片

那么，哪些不是爆米花电影呢？

各种看完会太爽、太不爽的或者看不完就睡着的影片

1 经典的剧情片，常说的奥斯卡级美国大片

2 恐怖、悬疑、鬼片

3 探讨精神病、伦理和社会问题的片子

4 革命影片

2012年6月7日星期四

也如丧了些什么

因为与众多同胞一样的原因，我从 blogger 消失了很久
今天偶尔上来看看，发现与 G+ 的整合已经让 blogger 功能焕然一新
重新来写几个字

前几天看高晓松的书，《如丧》
其实也没怎么认真看，文笔太犀利，措辞忒狠，不太适应
但这标题很引遐想
于是这些天来，一直觉得自己像是丧失了点什么东西，却又说不清楚的
反正我如丧的不是青春

2009年5月11日星期一

2009年4月16日星期四

parrot 鹦鹉 1.0 release

鹦鹉，对于 perl 6 意义重大
相当于真正执行二进制代码的虚拟机
如今，鹦鹉已经 release 了
但是很讽刺地，它现在的发展似乎明显超越了 perl 6 的开发进展

不管怎么说，它的正式发布，还是要恭喜的

2009年4月14日星期二

perl 参数的 I 和 i

perl 参数的 i 和 I 都可以指定路径
其中 I 指定的是文件夹
i 指定的是 pm 文件

比如 /Test 文件夹下有 Teacher.pl 和 Boy.pm 两个文件

../
./
|-Test/
  |-Boy.pm
  |-Teacher.pl

其中 Teacher.pl 调用 Boy.pm 代码
代码如下：


#!/cygdrive/c/Perl/bin/perl 

package Test::Teacher;
use strict;
use warnings;

use Test::Boy;

my @eth = Test::Boy::getEverything();

foreach(@eth){
print "out: ".$_."\n";
}
#!/cygdrive/c/Perl/bin/perl 
package Test::Boy;
use strict;
use warnings;

my @everything = 1 .. 9;

sub getEverything{
@everything;
}
1 假设当前路径为 /cygdrive/e/pl 时可以使用
perl Test/Teacher.pl
注：perl 会从 ./ 下寻找 Test::Boy.pm，也就是相当于 -iTest::Boy 参数

2 假设当前路径为 /cygdrive/e/pl/Test 时
则需要使用
perl -I../ Teacher.pl
注：perl 会从 ../ 寻找 Test::Boy.pm

use Foo::Bar 意味着什么
   ——摘自 http://wiki.perlchina.org/Simple_module_tutorial

use Foo::Bar
并不意味着在 @INC 的目录中寻找一个叫做Foo::Bar.pm的模块文件。
它的意思是在@INC的目录中寻找一个叫做‘Foo’的“子目录”，
然后在其中找一个叫做“Bar.pm”的“模块”。
现在，如果我们成功"use"了一个模块，
那么我们就可以通过完整的包路径语法
&PACKAGE::FUNCTION
使用这个模块中的所有函数。
当我们说&Foo::Bar::some_func的时候，
我们指的是“包的名字”而不是那个在use中曾使用的包含路径的文件名。
这会允许你可以在一个use过的文件中包含很多包名字。
实际使用中这些名字通常是相同的。


另外，假设 Teacher.pl 在 Test 文件夹同级

../
./
|test/
| |-Boy.pm
|-Teacher.pl

如果要调用 Boy.pm，也要在 Boy.pm 开头的 package 生命中写清
Test::Boy
即：pm 一定要放在 pm 内与包路径相同的文件夹下，并在文件夹外层调用

vim 7.0 也有 tab 页

古人云：vi 是个好东西

vi 的 buffer 是个不太好看的东西——中文真是博大精深，我主要表达的是不容易看清楚的意思
:ls 是个很好用的命令，但不够直观
用户一定要 ls 一下才能看清楚 buffer 里的东西
这样的操作显然违背了 vi 的特色——让人体任何部位的移动尽量减少，哪怕一毫米

于是，vim 7.0 开始支持 tab（标签页）
gvim 下的 tab 更是直观
最简单常用的用法如下：

netrw 中
t              把光标指向的文件在新标签页中打开
通常模式下
:tabnew          打开一个新的标签页
:tabc[lose]      关闭当前的标签页
:tab help         在一个新标签页中打开帮助
:help :tab        在帮助中打开关于标签页内容
:tab help :tab  在新标签页中打开关于新标签页的帮助

其他的，按以上方法查帮助吧

2009年4月13日星期一

perl socket

一个服务端

#!/cygdrive/c/Perl/bin/perl -w

use strict;
use warnings;

use IO::Socket;
use Tk;

sub sendf{
my $socket=IO::Socket::INET->;new(
       PeerHost      => 'localhost',
       Protor        => "tcp",
       PeerPort      => 3067
       );
die "no socket $@ \n" until $socket;
print "client created \n";

print $socket "client say: ".shift."\n";
$socket->;flush();
close($socket);
}

my $mw = MainWindow->;new;
$mw->;Button(    -text=>"say hello",    -command=>sub{sendf("Hello, server!");}    )->pack;

MainLoop;
一个客户端（只有一个按钮，按一下，就去跟服务器发消息）

#!/cygdrive/c/Perl/bin/perl 

use strict;
use warnings;

use Tk;
use IO::Socket;

my $socket = IO::Socket::INET->;new(
LocalHost      => 'localhost',
Proto          => "tcp",
LocalPort      => 3067,
Listen         => 5
) or die 'no socket $@ \n';
print "server created \n";

while(my $nsocket = $socket->;accept()){
while(defined (my $buf = <$nsocket>;))
{
   print "\n$buf";
}

}

close($socket);
print "server finished\n";

注意
服务器端 socket 创建时，listen 参数一定要设定，否则不会报错，但服务器不会被 accept() 阻塞

2009年4月11日星期六

sudo 功能不赘述，修改权限时，用 visudo 很安全——校验文件配置是否正确，如果不正确，在保存退出时就会提示你配置出错位置。
但我还是喜欢真正的vim。修改执行权限可以通过 vim：
vim /etc/sudoers

编辑中，支持别名（alias，跟变量差不多含义）

Alias主要分成4种
Host_Alias
Cmnd_Alias
User_Alias
Runas_Alias

1) 配置Host_Alias：就是主机的列表
Host_Alias HOST_FLAG = hostname1, hostname2, hostname3
2) 配置Cmnd_Alias：就是允许执行的命令的列表
Cmnd_Alias COMMAND_FLAG = command1, command2, command3
3) 配置User_Alias：就是具有sudo权限的用户的列表
User_Alias USER_FLAG = user1, user2, user3
4) 配置Runas_Alias：就是用户以什么身份执行（例如root，或者oracle）的列表
Runas_Alias RUNAS_FLAG = operator1, operator2, operator3
5) 实际上最终目标是要拼成如下格式
配置权限的格式如下：
USER_FLAG HOST_FLAG=(RUNAS_FLAG) COMMAND_FLAG
如果不需要密码验证的话，则按照这样的格式来配置
USER_FLAG HOST_FLAG=(RUNAS_FLAG) NOPASSWD: COMMAND_FLAG

配置示例：
# sudoers file.
#
# This file MUST be edited with the 'visudo' command as root.
#
# See the sudoers man page for the details on how to write a sudoers file.
#

# Host alias specification
Host_Alias EPG = 192.168.1.1, 192.168.1.2

# User alias specification

# Cmnd alias specification
Cmnd_Alias SQUID = /sbin/shutdown, /bin/rm

# Defaults specification

# User privilege specification
root ALL=(ALL) ALL
support EPG=(ALL) NOPASSWD: SQUID

# Uncomment to allow people in group wheel to run all commands
# %wheel ALL=(ALL) ALL

# Same thing without a password
# %wheel ALL=(ALL) NOPASSWD: ALL

# Samples
# %users ALL=/sbin/mount /cdrom,/sbin/umount /cdrom
# %users localhost=/sbin/shutdown -h now

注意
涉及到路径时最好写绝对路径
每行中间的空格，可以是 tab
保存后不需要重启，或者被修改帐户重新登录之类。直接使用就行

2009年3月31日星期二

openfire is very easy to use

本地试验，运行了个 xmpp 聊天服务器，很简单，很好用
openfire 作为服务器端，非常简单
中文控制台界面，足够了

2009年3月27日星期五

Debian 5 lost eth0

我弄丢了我虚拟机上的的 eth0！

最近我做得最大的动作，就是把我的 Debian 4 升级到 Debian5
——其实那已经是很久以前的事情了，但当时可能用的是 apt-get upgrade，所以不知不觉就升级上来了
当我突然发现版本号变化的时候，赶快去看了看这个最大版本号的升级带来了什么

我感兴趣的大概只有两件事
1. apt-get 系列改为 aptitude——仅凭这一点，就足以升级一个大版本号了
2. log 系统改为 rsyslog——其实这影响也不大，直接用 aptitude install 一下新的，就可以自动删除两个旧的 log 服务器了

以上更新完之后，重启
然后……我发现不能连接网络啦！！

ifconfig 的结果是只有 lo，没有eth0
这是一个很奇怪的现象，而这个现象显然不是来自系统升级——因为早就升级过了
刚做过的动作只是安装了 aptitude 和改变了 log 服务
但是这与网络没什么关系

上网查询了一下处理方法，有人说执行以下 dhconfig 就可以解决
试了一下，可行
但是重启之后还是要再次执行

很不甘心地检查了一下启动日志，发现出现了一个很诡异的 eth1
并且在 dhconfig 的时候，似乎也是通过配置 eth1 来使用网络的

目前问题原因仍在查询中，但更加合理的临时处理方案是，把
/etc/network/interfaces
文件里的 eth0 改成 eth1

这个方法对于有既存脚本针对 eth0 的人，显然不好用的
不过我可以暂时应付一下

另：
grep /var/log/kern.log
看到许多 udev: renamed network interface eth0 to eth1

2009年3月9日星期一

发现 Groovy

很眼馋 C++ 有 lua
我一直在寻找 Java 的脚本语言
最近发现 Groovy，也发现我不知道的脚本语言的用法——闭包

2009年2月5日星期四

perl cheatsheet(from perldoc)

下面是个关于 Perl 的 CheatSheet，也就是那种什么也没学的时候就先背下来，以后越学越受用的关键内容
格式……很讨厌，是从 perldoc 搞来的
blogger 的 css 让我搞了半天啊
绝对不做美工，果然要遭报应的……


CONTEXTS  SIGILS             ARRAYS        HASHES
  void      $scalar   whole:   @array        %hash
  scalar    @array    slice:   @array[0, 2]  @hash{'a', 'b'}
  list      %hash     element: $array[0]     $hash{'a'}
            &sub
            *glob    SCALAR VALUES
                     number, string, reference, glob, undef
  REFERENCES
  \     references      $$foo[1]       aka $foo->[1]
  $@%&* dereference     $$foo{bar}     aka $foo->{bar}
  []    anon. arrayref  ${$$foo[1]}[2] aka $foo->[1]->[2]
  {}    anon. hashref   ${$$foo[1]}[2] aka $foo->[1][2]
  \()   list of refs
                          NUMBERS vs STRINGS  LINKS
  OPERATOR PRECEDENCE     =          =        perl.plover.com
  ->                      +          .        search.cpan.org
  ++ --                   == !=      eq ne         cpan.org
  **                      < > <= >=  lt gt le ge   pm.org
  ! ~ \ u+ u-             <=>        cmp           tpj.com
  =~ !~                                            perldoc.com
  * / % x                 SYNTAX
  + - .                   for    (LIST) { }, for (a;b;c) { }
  << >>                   while  ( ) { }, until ( ) { }
  named uops              if     ( ) { } elsif ( ) { } else { }
  < > <= >= lt gt le ge   unless ( ) { } elsif ( ) { } else { }
  == != <=> eq ne cmp     for equals foreach (ALWAYS)
  &
  | ^              REGEX METACHARS            REGEX MODIFIERS
  &&               ^     string begin         /i case insens.
  ||               $     str. end (before \n) /m line based ^$
  .. ...           +     one or more          /s . includes \n
  ?:               *     zero or more         /x ign. wh.space
  = += -= *= etc.  ?     zero or one          /g global
  , =>             {3,7} repeat in range      /o cmpl pat. once
  list ops         ()    capture
  not              (?:)  no capture       REGEX CHARCLASSES
  and              []    character class  .  == [^\n]
  or xor           |     alternation      \s == whitespace
                   \b    word boundary    \w == word characters
                   \z    string end       \d == digits
  DO                                      \S, \W and \D negate
  use strict;        DON'T
  use warnings;      "$foo"           LINKS
  my $var;           $$variable_name  perl.com
  open() or die $!;  `$userinput`     use.perl.org
  use Modules;       /$userinput/     perl.apache.org

  FUNCTION RETURN LISTS
  stat      localtime    caller         SPECIAL VARIABLES
   0 dev    0 second     0 package      $_    default variable
   1 ino    1 minute     1 filename     $0    program name
   2 mode   2 hour       2 line         $/    input separator
   3 nlink  3 day        3 subroutine   $\    output separator
   4 uid    4 month-1    4 hasargs      $|    autoflush
   5 gid    5 year-1900  5 wantarray    $!    sys/libcall error
   6 rdev   6 weekday    6 evaltext     $@    eval error
   7 size   7 yearday    7 is_require   $$    process ID
   8 atime  8 is_dst     8 hints        $.    line number
   9 mtime               9 bitmask      @ARGV command line args
  10 ctime  just use                    @INC  include paths
  11 blksz  POSIX::      3..9 only      @_    subroutine args
  12 blcks  strftime!    with EXPR      %ENV  environment

Perl命令行应用介绍(转)

作者: Dave Cross
发表：August 10, 2004
原名: Perl Command-Line Options
原文：http://www.perl.com/pub/a/2004/08/09/commandline.html
译者: "Qiang":qiang

Perl 有很多命令行参数. 通过它, 我们有机会写出更简单的程序. 在这篇文章里我们来了解一些常用的参数.

Safety Net Options

在使用 Perl 尝试一些聪明( 或 stupid) 的想法时, 错误难免会发生. 有经验的 Perl 程序员常常使用三个参数来提前找到错误所在,

-C 是第一个. 这个参数编译 Perl 程序但不会真正运行它. 由此检查所有语法错误. 每次修改 perl 程序之后我都会立刻使用它来找到任何语法错误.

$ perl -c program.pl

-W 是第二个参数. 它会提示你任何潜在的问题. Perl 5.6.0 之后的版本已经用 use warnings; 替换了 -w .你应该使用 use warnings 因为它要比 -w 更灵活.
-T 是第三个参数. 它把 perl 放到了 tain 模式. 在这个模式里, Perl 会质疑任何程序外传来的数据. 例如,从命令行读取, 外部文件里读取或是 CGI 程序里传来的数据. 这些数据在 -T 模式里都会被 Tainted 掉.
Tainted 数据不可以被用来和外部交互. 例如使用在 system 调用和用作 open 的文件名. perlsec 文档里有更多什么数据会被Tainted 掉的例子.
要想使用 Tainted 的数据就需要 untaint这个数据. untaint 是通过正则表达式来实现.这里我不会太多的讲述 taint 模式. 如果你要编写的程序 (例如 CGI 程序) 需要从从用户那里接受不可知的输入, 我推荐使有 taint 模式

-d ,Perl Debugger , 在这里值得一提但我们无法顾及, 我推荐阅读文档 'perldoc perldebug' 或 Richard Foley 的 Perl Debugger Pocket Reference 一书.

Command-Line Programs

下面的几个 Perl 参数可以让短小的 Perl 程序运行在命令行. -e 可以让 Perl 程序在命令行上运行.例如, 我们可以在命令行上运行 "Hello World" 程序而不用把它写入文件再运行.

$ perl -e 'print "Hello World\n"'

多个 -e 也可以同时使用, 运行顺序根据它出现的位置.

$ perl -e 'print "Hello ";' -e 'print "World\n"'

象所有的 Perl 程序一样, 只有程序的最后一行不需要以 ; 结尾.
虽然你也可以象通常一样引用模块, 但 -M 让它变得更容易.

  $ perl -MLWP::Simple -e 'print head "http://www.example.com"'

-M模块名和 use 模块名一样. 如果不想引入模块的缺省值, 你可以使用 -m. -m模块名和 use 模块名() 一样. 例如下面这个例子, 因为 head 函数是缺省引入,而使用 -m 时就不会, 结果是没有输出.

  $ perl -mLWP::Simple -e 'print head "http://www.example.com"'

-m 和 -M 通过 = 来引入某个模块的特别函数.

 $ perl -MCGI=:standard -e 'print header'

这里, CGI.pm 的 ":standard" 被引入, header 函数因此可以使用.要引入多个参数可以通过使用引号和逗号.

$ perl -MCGI='header,start_html' -e 'print header, start_html'

这里我们引入了 header 和 start_html 函数.
Implicit Loops
-n 和 -p 增加了循环的功能, 使你可以一行一行来处理文件.

 $ perl -n -e 'some code' file1

这与下面的程序一样.

LINE:
  while (<>;) {
    # your code goes here
  }

<>; 打开命令行里的文件,一行行的读取.每一行缺省保存在 $_

  $ perl -n -e 'print "$. - $_"' file

上面的这一行可以写成

  LINE:
  while (<>;) {
    print "$. - $_"
  }

输出当前行数 $. 和当前行 $_.
-p 可以让上面的程序变得更容易. -p 会输出 $_ 就像这样

LINE:
  while (<>;) {
    # your code goes here
  } continue {
    print or die "-p destination: $!\n";
  }

continue 在这里保证print 在每次循环都会被调用.
使用 -p, 我们的打印行数程序可以改为

  $ perl -p -e '$_ = "$. - $_"'

注意到那个 LINE: 标签 ? 我们可以利用它来跳到下一个循环. 使用 next LINE

  $ perl -n -e 'next LINE unless /pattern/; print $_'

如果想在循环的前后做些处理, 可以使用 BEGIN 或 END block. 下面的这一行计算文件里的字数.

  $ perl -ne 'END { print $t } @w = /(\w+)/g; $t += @w' file.txt

每一行所有匹配的字放入数组 @w , 然后把 @w 的元素数目递加到 $t. END block 里的 print 最后输出文件总字数.
还有两个参数可以让这个程序变得更简单. -a 打开自动分离 (split) 模式. 空格是缺省的分离号. 输入根据分离号被分离然后放入缺省数组 @F. 由此,我们可以把上面的程序改写为

$ perl -ane 'END {print $x} $x += @F' file.txt

你也可以通过 -F 把缺省的分离号改为你想要的.例如把分离号定为非字符:

$ perl -F'\W' -ane 'END {print $x} $x += @F' file.txt

下面通过 Unix password 文件来介绍一个复杂的例子. Unix password 是文本文件, 每一行是一个用户记录, 由冒号 : 分离. 第 7 行是用户的登录 shell 路径. 我们可以得出每一个不同 shell 路径被多少个用户使用 :

  $ perl -F':' -ane '$s{$F[6]}++;' \
>; -e 'END { print "$_ : $s{$_}" for keys %s }' /etc/passwd

虽然现在不是一行, 但是你可以看出使用参数可以解决什么问题.
Record Separators
以前我提到过 $/ 和 $\ -- 输入,输出分隔号. $/ 用来分隔从文件句柄里读出的数据, 缺省 $/ 分隔号是 \n , 这样每次从文件句柄里就会一行行的读取. $\ 缺省是空字符, 用来自动加到要 print 的数据尾端. 这就是为什么很多时候 print 都要在末尾加上 \n.
$/ 和 $\ 可与 -n -p 一起使用. 在命令行上相对应为 -0 (零) 和 -l ( 这是 L ). -0 后面可以跟一个 16 进制或8进制数值, 这个值用来付给 $/ . -00 打开段落模式, -0777 打开slurp 模式 (即可以一次把整个文件读入) , 这与把 $/ 设为空字符和 undef 一样效果.
单独使用 -l 有两个效果, 第一自动 chomp 输入分隔号, 第二把$/ 值付给 $\ ( 这样 print 的时候就会自动在末尾加 \n )
我个人常常使用 -l 参数, 用来给每一个输出加 \n. 例如

$ perl -le 'print "Hello World"'

In-Place Editing
使用已有的参数我们可以写出很有效的命令行程序. 常见的Unix I/O 重定向:

 $ perl -pe 'some code' <>; output.txt

这个程序从 input.txt 读取数据, 然后做一些处理再输出到 output.txt. 你当然也可以把输出重定向到同一个文件里.
上面的程序可以通过 -i 参数做的更简单些. -i 把源文件更名然后从这个更名的源文件里读取.最后把处理后的数据写入源文件. 如果 -i 后跟有其他字符串, 这个字符串与源文件名合成后来生成一个新的文件名. 此文件会被用来储存原始文件以免被 -i 参数覆盖.
这个例子把所有 php 字符替换为 perl :

$ perl -i -pe 's/\bPHP\b/Perl/g' file.txt

程序读取文件的每一行, 然后替换字符, 处理后的数据重新写入( 即覆盖 ) 源文件. 如果不想覆盖源文件, 可以使用

$perl -i.bak -pe 's/\bPHP\b/Perl/g' file.txt

这里处理过的数据写入 file.txt , file.txt.bak 是源文件的备份.

2009年2月4日星期三

归来

2009年，春节，和莹莹去了一趟西双版纳
见识了云，见识了山，见识了漂亮的大蝴蝶
酸甜苦辣的一趟旅程，是美丽生活的小插曲

2008年12月18日星期四

失败只要几次

blogger 已经很久不来了，因为曾经非常的不好用，又要代理又要什么的
后来旧习惯了不来，明知道 blogger 会不错的，也没心情再来尝试
所以，要想干掉一个网站，只要他的用户，体验几次失败，就不会再来了
突然想到前阵子视频网站牌照风波，似乎有些商家就是停止了一段时间，就再也回不来了

所以要想毁掉大家对一件事情的信心，只要让他们体验几次失败，就足够了

2007年6月12日星期二

JavaScript Tutorial

JavaScript Tutorial ——指南

JavaScript is the scripting language of the Web! JavaScript是一种工作在Web页面的脚本语言！

JavaScript is used in millions of Web pages to improve the design, validate forms, detect browsers, create cookies, and much more.

JavaScript已经在无数Web页面发挥着作用，他们提升设计效果、验证表单、检测浏览器、创建cookies，等等等等。

JavaScript is the most popular scripting language on the internet. JavaScript是Internet上最流行的脚本语言。

JavaScript is easy to learn! You will enjoy it! JavaScript容易上手！您可以轻松享受！

Start learning JavaScript now! 现在开始学习JavaScript！

JavaScript Examples ——举例

Learn by 100 examples! With our editor, you can edit the source code, and click on a test button to view the result.

JavaScript学习100例！通过你的编辑器，您可以编辑源代码，并通过点击测试键（test）看到结果。

JavaScript Quiz Test ——测试

Test your JavaScript skills at W3Schools!

在W3Schools测试您的JavaScript技术！

Start JavaScript Quiz! 开始测试JavaScript

JavaScript References ——JavaScript说明（rfc?）

At W3Schools you will find complete references of all JavaScript objects and the HTML DOM objects.

您可以在W3Schools找到全部JavaScript的对象和HTML Dom 对象的完整文档。

JavaScript介绍

JavaScript is used in millions of Web pages to improve the design, validate forms, detect browsers, create cookies, and much more.

JavaScript已经在无数Web页面发挥着作用，他们提升设计效果、验证表单、检测浏览器、创建cookies，等等等等

JavaScript is the most popular scripting language on the internet, and works in all major browsers, such as Internet Explorer, Mozilla, Firefox, Netscape, and Opera.

JavaScript是Internet上最流行的脚本语言，并且在主流浏览器上都能运行，比如IE，Mozilla，Firefox,Netscape，Opera。

What You Should Already Know ——需要首先掌握的知识

Before you continue you should have a basic understanding of the following:

在您开始学习之前，首先应该对下列知识有一些了解

HTML / XHTML

If you want to study these subjects first, find the tutorials on our Home page.

如果您打算先学习这些课题，可以在我们的主页上找到相关指南

What is JavaScript?JavaScript是什么？

JavaScript was designed to add interactivity to HTML pages

JavaScript是为了增强HTML页面的交互性而出现的

JavaScript is a scripting language

JavaScript是一种脚本语言

A scripting language is a lightweight programming language

脚本语言是一种轻量级的程序语言

A JavaScript consists of lines of executable computer code

JavaScript最终成为可执行的机器代码中的一部分

A JavaScript is usually embedded directly into HTML pages

JavaScript通常直接嵌入到HTML页面中

JavaScript is an interpreted language (means that scripts execute without preliminary compilation)

JavaScript是一种解释性语言（这意味着脚本的执行将不需要进行另外的编译）

Everyone can use JavaScript without purchasing a license

任何人都可以使用JavaScript而不需要购买什么许可^_^

Are Java and JavaScript the Same? Java和JavaScript一样么？

NO!

不一样！

Java and JavaScript are two completely different languages in both concept and design!

无论是从概念还是从设计上看，Java与JavaScript都是两种完全不同的语言

Java (developed by Sun Microsystems) is a powerful and much more complex programming language - in the same category as C and C++.

Java（Sun公司设计出来的东西）是一种强大的并且十分复杂的程序语言——与C、C++属于同一家族

What can a JavaScript Do? JavaScript能做什么？

JavaScript gives HTML designers a programming tool - HTML authors are normally not programmers, but JavaScript is a scripting language with a very simple syntax! Almost anyone can put small "snippets" of code into their HTML pages

JavaScript为HTML设计人员提供了一种编程工具——HTML作者通常并不是程序员，而JavaScript这种脚本语言使用的语法非常简单！啥人都能在HTML页面中写这么个小玩意儿出来

JavaScript can put dynamic text into an HTML page - A JavaScript statement like this: document.write("<h1>" + name + "</h1>") can write a variable text into an HTML page

JavaScript可以把动态文本插入到HTML页面中——如果想写入一段动态文本，JavaScript段就是是介个样子滴：document.write("<h1>" + name + "</h1>")

JavaScript can react to events - A JavaScript can be set to execute when something happens, like when a page has finished loading or when a user clicks on an HTML element

可以通过时间重新激活JavaScript——可以设定JavaScript在某件事情发生时随之执行，比如页面载入完成啦，或者用户点击了HTML上的什么东东啦

JavaScript can read and write HTML elements - A JavaScript can read and change the content of an HTML element

JavaScript可以对HTML元素进行读写——JavaScript可以读取甚至改变HTML元素的内容

JavaScript can be used to validate data - A JavaScript can be used to validate form data before it is submitted to a server. This saves the server from extra processing

JavaScript可以拿来验证数据——在表单提交到数据库之前，我们可以用JavaScript来验证表单数据。这样做可以降低服务器的负荷

JavaScript can be used to detect the visitor's browser - A JavaScript can be used to detect the visitor's browser, and - depending on the browser - load another page specifically designed for that browser

JavaScript可以检测访问者的浏览器——JavaScript可以检测访问者的浏览器，并且加载一个为这个浏览器设计的页面

JavaScript can be used to create cookies - A JavaScript can be used to store and retrieve information on the visitor's computer

JavaScript可以创建cookies——JavaScript可以存储和查询存放在访问者的电脑中的（cookies）信息

JavaScript 应该怎么写

The HTML <script> tag is used to insert a JavaScript into an HTML page.

HTML中使用<script>标签将JavaScript插入到HTML页面中。

Examples 例子

Write text 写一段文本
How to write text on a page. 如何在页面上写一段文字。

Write text with formatting 写带格式的文本
How to format the text on your page with HTML tags. 如何在你的页面上使用HTML标签写一段带格式的文本内容。

How to Put a JavaScript Into an HTML Page 如何把一段JavaScript代码加入到HTML页面中

<html>
<body>
<script type="text/javascript">
document.write("Hello World!")
</script>
</body>
</html>

The code above will produce this output on an HTML page: 上面这段代码将在HTML页面上产生这样一段输出效果：

Hello World!

Example Explained 例子解释

To insert a JavaScript into an HTML page, we use the <script> tag (also use the type attribute to define the scripting language).

我们可以通过<script> 标签将JavaScript插入到HTML页面中。（同时还要用 type 属性定义使用的脚本语言）

So, the <script type="text/javascript"> and </script> tells where the JavaScript starts and ends:

像这样用<script type="text/javascript">和</script>声明JavaScript的起止：

<html>
<body>
<script type="text/javascript">
...
</script>
</body>
</html>

The word document.write is a standard JavaScript command for writing output to a page.

document.write 这段字是JavaScript向页面输出内容的标准命令。

By entering the document.write command between the <script type="text/javascript"> and </script> tags, the browser will recognize it as a JavaScript command and execute the code line. In this case the browser will write Hello World! to the page:

通过在 <script type="text/javascript"> 和 </script> 标签之间输入 document.write 命令，浏览器会自动识别这段JavaScript命令并执行。下面演示了通过这种方法在页面中输出Hello world！

<html>
<body>
<script type="text/javascript">
document.write("Hello World!")
</script>
</body>
</html>

Note: If we had not entered the <script> tag, the browser would have treated the document.write("Hello World!") command as pure text, and just write the entire line on the page.

注意：如果我们没有输入<script>标签，浏览器会将 document.write("Hello World!") 这段命令当作一段纯文本内容，并且直接把这条命令整行输出到页面上。

Ending Statements With a Semicolon? 用分号作语句结尾？

With traditional programming languages, like C++ and Java, each code statement has to end with a semicolon.

像C++和Java这类复杂的程序语言中，通常是用分号作为一个表达式或者语句的结尾

Many programmers continue this habit when writing JavaScript, but in general, semicolons are optional! However, semicolons are required if you want to put more than one statement on a single line.

在写JavaScript的时候很多程序员希望保留这种习惯，尽管分号并不是必需的，然而，当您输入的是不止一个语句的时候，那么使用分号仍然是必要的。

How to Handle Older Browsers 老版本浏览器怎么办

Browsers that do not support JavaScript will display the script as page content. To prevent them from doing this, we may use the HTML comment tag:

不支持JavaScript的浏览器会把脚本作为页面内容输出的。要防止这种情况，我们可以使用下面这个HTML标签：

<script type="text/javascript">
<!--
document.write("Hello World!")
//-->
</script>

The two forward slashes at the end of comment line (//) are a JavaScript comment symbol. This prevents the JavaScript compiler from compiling the line.

命令行前面的两个正斜杠是JavaScript的注释标记。这将防止JavaScript编译器编译这一行。

JavaScript 应该写在哪

JavaScripts in the body section will be executed WHILE the page loads. 写在body段里的JavaScript会在页面读取过程中执行。

JavaScripts in the head section will be executed when CALLED. 写在head段里的JavaScript会在被调用的时候执行

Examples 例子

Head section
Scripts that contain functions go in the head section of the document. Then we can be sure that the script is loaded before the function is called.

包含函数的脚本写在文档的head段。在函数被调用之前，脚本就已经被加载好了，可以随时调用

Body section
Execute a script that is placed in the body section.

执行放在body段里的脚本。

External script
How to access an external script.

如何访问外部脚本。

Where to Put the JavaScript 该把JavaScript放在哪

JavaScripts in a page will be executed immediately while the page loads into the browser. This is not always what we want. Sometimes we want to execute a script when a page loads, other times when a user triggers an event.

可能有时候我们会对JavaScript的执行时间有些自己的想法：有时候我们不希望页面上的JavaScript在浏览器加载的时候立刻执行，但也可能有时候我们希望在页面加载的时候就执行一些脚本。

Scripts in the head section: Scripts to be executed when they are called, or when an event is triggered, go in the head section. When you place a script in the head section, you will ensure that the script is loaded before anyone uses it.

写在和head段的脚本：head段里的脚本在被调用的时候执行，或者在事件被触发的时候执行。不过放在head段的脚本，却是在被调用前就加载好的。

<html>
<head>
<script type="text/javascript">
....
</script>
</head>

Scripts in the body section: Scripts to be executed when the page loads go in the body section. When you place a script in the body section it generates the content of the page.

body段的脚本：body段里的脚本在页面加载的时候就立刻执行了。当你把脚本放在body段里的时候，它会生成一些页面的内容。

<html>
<head>
</head>
<body>
<script type="text/javascript">
....
</script>
</body>

Scripts in both the body and the head section: You can place an unlimited number of scripts in your document, so you can have scripts in both the body and the head section.

body和head段都可以有脚本：你可以在你的文档中安排若干个脚本，所以在head和body段里可以同时各自写有脚本。

<html>
<head>
<script type="text/javascript">
....
</script>
</head>
<body>
<script type="text/javascript">
....
</script>
</body>

Using an External JavaScript 使用外部JavaScript

Sometimes you might want to run the same JavaScript on several pages, without having to write the same script on every page.

有时您可能想要在不同的页面执行同一个Javascript，而又不想在每一个页面分别写一次同样的脚本。

To simplify this, you can write a JavaScript in an external file. Save the external JavaScript file with a .js file extension.

为了简化这种工作，您可以使用外部JavaScript。把外部JavaScript文件保存到一个以.js为扩展名的文件中。

Note: The external script cannot contain the <script> tag!

注意：在外部脚本里不能包含<script>标签！

To use the external script, point to the .js file in the "src" attribute of the <script> tag:

使用外部脚本时，需要在<script>标签中将.js文件在“src”属性中指明：

<html>
<head>
<script src="xxx.js"></script>
</head>
<body>
</body>
</html>

Note: Remember to place the script exactly where you normally would write the script!

注意：记得把脚本放在你平时写脚本的地方

JavaScript 中的变量

A variable is a "container" for information you want to store.

变量是您用来存储信息的容器。

Examples 例子

Variable 变量
Variables are used to store data. This example will show you how.

变量是用来存储数据的。这个例子向您展示如何使用。

Variables 变量

A variable is a "container" for information you want to store. A variable's value can change during the script. You can refer to a variable by name to see its value or to change its value.

变量是您用来存储信息的一个容器。在脚本执行过程中，变量的值是可以改变的。无论值怎么变，您都可以通过变量名来使用这个变量。

Rules for variable names: 变量命名规则：

Variable names are case sensitive 变量名是大小写敏感的
They must begin with a letter or the underscore character 必须以字母或下划线开头

IMPORTANT! JavaScript is case-sensitive! A variable named strname is not the same as a variable named STRNAME!

重要信息！JavaScript是大小写敏感的！比如strname和STRNAME这两个变量是不一样的！

Declare a Variable 声明变量

You can create a variable with the var statement: 您可以通过下述var语句建立变量：

var strname = some value

You can also create a variable without the var statement: 您也可以通过这种没有var的语句建立变量

strname = some value

Assign a Value to a Variable 给变量赋值

You can assign a value to a variable like this: 可以这样赋值：

var strname = "Hege"

Or like this: 这样也行：

strname = "Hege"

The variable name is on the left side of the expression and the value you want to assign to the variable is on the right. Now the variable "strname" has the value "Hege".

变量名必须写在赋值表达式左边。

Lifetime of Variables 变量的生命周期

When you declare a variable within a function, the variable can only be accessed within that function. When you exit the function, the variable is destroyed. These variables are called local variables. You can have local variables with the same name in different functions, because each is recognized only by the function in which it is declared.

当您在一个函数中声明了一个变量，那么这个变量只能在函数内部使用，函数结束的时候这个变量就被销毁。这叫做局部变量。您也可以在不同函数中用相同的变量名再声明一个变量，因为只有在函数内部才能识别这个变量。

If you declare a variable outside a function, all the functions on your page can access it. The lifetime of these variables starts when they are declared, and ends when the page is closed.

如果您在函数外部声明了一个变量，那么所有的函数都能访问这个变量。这个变量的生命周期从声明时开始，直到页面关闭时才结束。

JavaScript If...Else 条件表达式

Conditional statements in JavaScript are used to perform different actions based on different conditions.

JavaScript的条件表达式用来对不同条件作出不同响应。

Examples 例子

If statement If 表达式
How to write an if statement. 如何写if表达式

If...else statement If...else表达式
How to write an if...else statement. 如何写if...else表达式。

If..else if...else statement If..else if...else表达式
How to write an if..else if...else statement. 如何写 if..else if...else 表达式

Random link 随即链接
This example demonstrates a link, when you click on the link it will take you to W3Schools.com OR to RefsnesData.no. There is a 50% chance for each of them.

这个例子演示了一个链接，当您点击这个链接的时候，它将带您到 W3Schools.com 或者 RefsnesData.no。各有50%机率。

Conditional Statements 条件表达式

Very often when you write code, you want to perform different actions for different decisions. You can use conditional statements in your code to do this.

在您写代码的时候，经常需要面对不同选择做出不同响应。这时您可以使用判断语句。

In JavaScript we have the following conditional statements:

在JavaScript中，我们可以使用下列判断语句

if statement - use this statement if you want to execute some code only if a specified condition is true
if 语句 - 如果您只是想制定当某一状态为true时需要执行操作，则使用这种语句
if...else statement - use this statement if you want to execute some code if the condition is true and another code if the condition is false
if...else 语句 - 如果您想分别针对状态为真或假时指定动作，则使用这种语句
if...else if....else statement - use this statement if you want to select one of many blocks of code to be executed
if...else if....else 语句 - 如果你想对多种情况择一运行，则使用这种语句
switch statement - use this statement if you want to select one of many blocks of code to be executed
switch 语句 - 效果与前一种类似，但语法不同

If Statement

You should use the if statement if you want to execute some code only if a specified condition is true.

Syntax

if (condition)
{
code to be executed if condition is true }

Note that if is written in lowercase letters. Using uppercase letters (IF) will generate a JavaScript error!

Example 1

<script type="text/javascript">
//Write a "Good morning" greeting if
//the time is less than 10 var d=new Date() var time=d.getHours() if (time<10)  { document.write("<b>Good morning</b>") } </script>

Example 2

<script type="text/javascript">
//Write "Lunch-time!" if the time is 11 var d=new Date() var time=d.getHours() if (time==11)  { document.write("<b>Lunch-time!</b>") } </script>

Note: When comparing variables you must always use two equals signs next to each other (==)!

Notice that there is no ..else.. in this syntax. You just tell the code to execute some code only if the specified condition is true.

If...else Statement

If you want to execute some code if a condition is true and another code if the condition is not true, use the if....else statement.

Syntax

if (condition)
{
code to be executed if condition is true } else { code to be executed if condition is not true }

Example

<script type="text/javascript">
//If the time is less than 10,
//you will get a "Good morning" greeting.
//Otherwise you will get a "Good day" greeting. var d = new Date() var time = d.getHours() if (time < 10)  { document.write("Good morning!") } else { document.write("Good day!") } </script>

If...else if...else Statement

You should use the if....else if...else statement if you want to select one of many sets of lines to execute.

Syntax

if (condition1)
{
code to be executed if condition1 is true } else if (condition2)
{
code to be executed if condition2 is true } else { code to be executed if condition1 and condition2 are not true }

Example

<script type="text/javascript">
var d = new Date()
var time = d.getHours()
if (time<10)
{
document.write("<b>Good morning</b>")
}
else if (time>10 && time<16)
{
document.write("<b>Good day</b>")
}
else
{
document.write("<b>Hello World!</b>")
}
</script>

JavaScript的Switch 语句

Conditional statements in JavaScript are used to perform different actions based on different conditions.

Examples

Switch statement
How to write a switch statement.

The JavaScript Switch Statement

You should use the switch statement if you want to select one of many blocks of code to be executed.

Syntax

switch(n)
{
case 1:
  execute code block 1   break     case 2:   execute code block 2   break default:   code to be executed if n is   different from case 1 and 2 }

This is how it works: First we have a single expression n (most often a variable), that is evaluated once. The value of the expression is then compared with the values for each case in the structure. If there is a match, the block of code associated with that case is executed. Use break to prevent the code from running into the next case automatically.

Example

<script type="text/javascript">
//You will receive a different greeting based
//on what day it is. Note that Sunday=0,
//Monday=1, Tuesday=2, etc. var d=new Date() theDay=d.getDay() switch (theDay) { case 5:   document.write("Finally Friday")   break case 6:   document.write("Super Saturday")   break case 0:   document.write("Sleepy Sunday")   break default:   document.write("I'm looking forward to this weekend!") } </script>

JavaScript 操作符

Arithmetic Operators

Operator	Description	Example	Result
+	Addition 加法	x=2 y=2 x+y	4
-	Subtraction 减法	x=5 y=2 x-y	3
*	Multiplication 乘法	x=5 y=4 x*y	20
/	Division 除法	15/5 5/2	3 2.5
%	Modulus (division remainder) 取模(余)	5%2 10%8 10%2	1 2 0
++	Increment 自增	x=5 x++	x=6
--	Decrement 自减	x=5 x--	x=4

Assignment Operators

Operator	Example	Is The Same As
=	x=y	x=y
+=	x+=y	x=x+y
-=	x-=y	x=x-y
*=	x*=y	x=x*y
/=	x/=y	x=x/y
%=	x%=y	x=x%y

Comparison Operators 比较运算符

Operator	Description	Example
==	is equal to 相等	5==8 returns false
===	is equal to (checks for both value and type) 相等（同时检查值与类型）	x=5 y="5" x==y returns true x===y returns false
!=	is not equal 不等	5!=8 returns true
>	is greater than 大于	5>8 returns false
<	is less than 小于	5<8 returns true
>=	is greater than or equal to 大于等于	5>=8 returns false
<=	is less than or equal to 小于等于	5<=8 returns true

Logical Operators

Operator	Description	Example
&&	and 与	x=6 y=3 (x < 10 && y > 1) returns true
\|\|	or 或	x=6 y=3 (x==5 \|\| y==5) returns false
!	not 非	x=6 y=3 !(x==y) returns true

Operator

Description

Example

and 与

x=6
y=3

(x < 10 && y > 1) returns true

or 或

x=6
y=3

(x==5 || y==5) returns false

not 非

x=6
y=3

!(x==y) returns true

String Operator 字符串操作符

A string is most often text, for example "Hello World!". To stick two or more string variables together, use the + operator.
字符串时最常用的文字类型，例如：“Hello World！”。可以用两个字符串直接使用“+”号相加

txt1="What a very"
txt2="nice day!"
txt3=txt1+txt2

The variable txt3 now contains "What a verynice day!".
这时，变量txt3中的内容是“What a verynice day!”。

To add a space between two string variables, insert a space into the expression, OR in one of the strings.

txt1="What a very"
txt2="nice day!"
txt3=txt1+" "+txt2 or txt1="What a very " txt2="nice day!" txt3=txt1+txt2

The variable txt3 now contains "What a very nice day!".

Conditional Operator

JavaScript also contains a conditional operator that assigns a value to a variable based on some condition.

Syntax

variablename=(condition)?value1:value2

Example

greeting=(visitor=="PRES")?"Dear President ":"Dear "

If the variable visitor is equal to PRES, then put the string "Dear President " in the variable named greeting. If the variable visitor is not equal to PRES, then put the string "Dear " into the variable named greeting.

JavaScript弹出对话框

In JavaScript we can create three kinds of popup boxes: Alert box, Confirm box, and Prompt box.
在JavaScript中，我们可以创建三中弹出式对话框：警告，提醒，和对话框

Examples

Alert box

Alert box with line breaks

Confirm box

Prompt box

Alert Box

An alert box is often used if you want to make sure information comes through to the user.

When an alert box pops up, the user will have to click "OK" to proceed.

Syntax:

alert("sometext")

Confirm Box

A confirm box is often used if you want the user to verify or accept something.
如果您想判断用户对某事是否进行确认或接受，可以使用确认框

When a confirm box pops up, the user will have to click either "OK" or "Cancel" to proceed.
弹出确认框时，将对用户点击OK或Cancel进行处理

If the user clicks "OK", the box returns true. If the user clicks "Cancel", the box returns false.
如果用户点击OK，返回值为true。如果用户点击Cancel，返回值为false

Syntax:

confirm("sometext")

Prompt Box

A prompt box is often used if you want the user to input a value before entering a page.

When a prompt box pops up, the user will have to click either "OK" or "Cancel" to proceed after entering an input value.

If the user clicks "OK" the box returns the input value. If the user clicks "Cancel" the box returns null.
用户点击OK是返回输入的值。用户点击Cancel时返回值为空

Syntax:

prompt("sometext","defaultvalue")

JavaScript函数

A function is a reusable code-block that will be executed by an event, or when the function is called.
函数是一个代码块，在被函数或事件调用时被整体执行。

Examples

Function
How to call a function.

Function with arguments
How to pass a variable to a function, and use the variable in the function.

Function with arguments 2
How to pass variables to a function, and use these variables in the function.

Function that returns a value
How to let the function return a value.

A function with arguments, that returns a value
How to let the function find the product of 2 arguments and return the result.

JavaScript 函数

To keep the browser from executing a script as soon as the page is loaded, you can write your script as a function.
浏览器载入页面时，不会立刻执行写在函数中的代码。

A function contains some code that will be executed only by an event or by a call to that function.
函数中的代码只有在函数被调用的时候才会执行，比如触发事件之类的。

You may call a function from anywhere within the page (or even from other pages if the function is embedded in an external .js file).
任何东东都可以调用函数，但不能超出页面范围（有一种例外：函数被写在“.js”后缀的文件中时，文件可以被其他页面调用）

Functions are defined at the beginning of a page, in the <head> section.
函数定义应该写在页面的开头，也就是<head>段中。

Example

<html>
<head>
<script type="text/javascript">
function displaymessage()
{
alert("Hello World!")
}
</script>
</head> <body> <form> <input type="button" value="Click me!" onclick="displaymessage()" > </form> </body> </html>

If the line: alert("Hello world!!"), in the example above had not been written within a function, it would have been executed as soon as the line was loaded. Now, the script is not executed before the user hits the button. We have added an onClick event to the button that will execute the function displaymessage() when the button is clicked.

You will learn more about JavaScript events in the JS Events chapter.

如何定义一个函数

The syntax for creating a function is:

function functionname(var1,var2,...,varX)
{
some code }

var1, var2, etc are variables or values passed into the function. The { and the } defines the start and end of the function.

Note: A function with no parameters must include the parentheses () after the function name:

function functionname()
{
some code }

Note: Do not forget about the importance of capitals in JavaScript! The word function must be written in lowercase letters, otherwise a JavaScript error occurs! Also note that you must call a function with the exact same capitals as in the function name.

返回语句

The return statement is used to specify the value that is returned from the function.

So, functions that are going to return a value must use the return statement.

Example

The function below should return the product of two numbers (a and b):

function prod(a,b)
{
x=a*b
return x
}

When you call the function above, you must pass along two parameters:

product=prod(2,3)

The returned value from the prod() function is 6, and it will be stored in the variable called product.

JavaScript的For循环

Loops in JavaScript are used to execute the same block of code a specified number of times or while a specified condition is true.

Examples

For loop
How to write a for loop. Use a For loop to run the same block of code a specified number of times.

Looping through HTML headers
How to use the for loop to loop through the different HTML headers.

JavaScript Loops

Very often when you write code, you want the same block of code to run over and over again in a row. Instead of adding several almost equal lines in a script we can use loops to perform a task like this.

In JavaScript there are two different kind of loops:

for - loops through a block of code a specified number of times
while - loops through a block of code while a specified condition is true

The for Loop

The for loop is used when you know in advance how many times the script should run.

Syntax

for (var=startvalue;var<=endvalue;var=var+increment) 
{
    code to be executed }

Example

Explanation: The example below defines a loop that starts with i=0. The loop will continue to run as long as i is less than, or equal to 10. i will increase by 1 each time the loop runs.

Note: The increment parameter could also be negative, and the <= could be any comparing statement.

<html>
<body>
<script type="text/javascript">
var i=0
for (i=0;i<=10;i++)
{
document.write("The number is " + i)
document.write("<br />")
}
</script>
</body>
</html>

Result

The number is 0
The number is 1
The number is 2
The number is 3
The number is 4
The number is 5
The number is 6
The number is 7
The number is 8
The number is 9
The number is 10

The while loop

The while loop will be explained in the next chapter.

JavaScript的While循环

Loops in JavaScript are used to execute the same block of code a specified number of times or while a specified condition is true.

Examples

While loop
How to write a while loop. Use a while loop to run the same block of code while a specified condition is true.

Do while loop
How to write a do...while loop. Use a do...while loop to run the same block of code while a specified condition is true. This loop will always be executed at least once, even if the condition is false, because the statements are executed before the condition is tested.

The while loop

The while loop is used when you want the loop to execute and continue executing while the specified condition is true.

while (var<=endvalue)
{
    code to be executed }

Note: The <= could be any comparing statement.

Example

Explanation: The example below defines a loop that starts with i=0. The loop will continue to run as long as i is less than, or equal to 10. i will increase by 1 each time the loop runs.

<html>
<body>
<script type="text/javascript">
var i=0
while (i<=10)
{
document.write("The number is " + i)
document.write("<br />")
i=i+1
}
</script>
</body>
</html>

Result

The number is 0
The number is 1
The number is 2
The number is 3
The number is 4
The number is 5
The number is 6
The number is 7
The number is 8
The number is 9
The number is 10

The do...while Loop

The do...while loop is a variant of the while loop. This loop will always execute a block of code ONCE, and then it will repeat the loop as long as the specified condition is true. This loop will always be executed at least once, even if the condition is false, because the code is executed before the condition is tested.

do
{
    code to be executed } while (var<=endvalue)

Example

<html>
<body>
<script type="text/javascript">
var i=0
do 
{
document.write("The number is " + i)
document.write("<br />")
i=i+1
}
while (i<0)
</script>
</body>
</html>

Result

The number is 0

JavaScript的中止和继续

There are two special statements that can be used inside loops: break and continue.

Examples

Break statement
Use the break statement to break the loop.

Continue statement
Use the continue statement to break the current loop and continue with the next value.

JavaScript break and continue Statements

There are two special statements that can be used inside loops: break and continue.

Break

The break command will break the loop and continue executing the code that follows after the loop (if any).

Example

<html>
<body>
<script type="text/javascript">
var i=0
for (i=0;i<=10;i++)
{
if (i==3){break}
document.write("The number is " + i)
document.write("<br />")
}
</script>
</body>
</html>

Result

The number is 0
The number is 1
The number is 2

Continue

The continue command will break the current loop and continue with the next value.

Example

<html>
<body>
<script type="text/javascript">
var i=0
for (i=0;i<=10;i++)
{
if (i==3){continue}
document.write("The number is " + i)
document.write("<br />")
}
</script>
</body>
</html>

Result

The number is 0
The number is 1
The number is 2
The number is 4
The number is 5
The number is 6
The number is 7
The number is 8
The number is 9
The number is 10

JavaScript的For...In语句

The for...in statement is used to loop (iterate) through the elements of an array or through the properties of an object.

Examples

For...In statement
How to use a for...in statement to loop through the elements of an array.

JavaScript For...In Statement

The for...in statement is used to loop (iterate) through the elements of an array or through the properties of an object.

The code in the body of the for ... in loop is executed once for each element/property.

Syntax

for (variable in object)
{
    code to be executed }

The variable argument can be a named variable, an array element, or a property of an object.

Example

Using for...in to loop through an array:

<html>
<body> <script type="text/javascript"> var x var mycars = new Array() mycars[0] = "Saab" mycars[1] = "Volvo" mycars[2] = "BMW" for (x in mycars) { document.write(mycars[x] + "<br />") } </script> </body> </html>

JavaScript事件

Events are actions that can be detected by JavaScript.
事件，是可以被JavaScript检测到的动作：

Events

By using JavaScript, we have the ability to create dynamic web pages. Events are actions that can be detected by JavaScript.
通过使用JavaScript，我们可以创建web页面。事件是可以被JavaScript检测到的动作。

Every element on a web page has certain events which can trigger JavaScript functions. For example, we can use the onClick event of a button element to indicate that a function will run when a user clicks on the button. We define the events in the HTML tags.
每一个页面元素都有一些特定的事件可以激活JavaScript函数。例如，我们可以使用按钮元素的onClick事件响应用户的点击动作。我们在HTML标签中定义这些事件。

Examples of events:
事件举例：

A mouse click 鼠标点击
A web page or an image loading 页面或图像载入
Mousing over a hot spot on the web page 鼠标划过页面的某些hot spot?
Selecting an input box in an HTML form 在HTML表单中选择了一个输入框
Submitting an HTML form 提交HTML表单
A keystroke @#￥%某个什么东西……

Note: Events are normally used in combination with functions, and the function will not be executed before the event occurs!
注意：事件通常用来激活某个函数，而这个函数在事件发生前并不运行。

For a complete reference of the events recognized by JavaScript, go to our complete Event reference.
在我们的完整事件说明中，有JavaScript支持的全部事件的介绍

onload and onUnload

The onload and onUnload events are triggered when the user enters or leaves the page.

The onload event is often used to check the visitor's browser type and browser version, and load the proper version of the web page based on the information.

Both the onload and onUnload events are also often used to deal with cookies that should be set when a user enters or leaves a page. For example, you could have a popup asking for the user's name upon his first arrival to your page. The name is then stored in a cookie. Next time the visitor arrives at your page, you could have another popup saying something like: "Welcome John Doe!".

onFocus, onBlur and onChange

The onFocus, onBlur and onChange events are often used in combination with validation of form fields.

Below is an example of how to use the onChange event. The checkEmail() function will be called whenever the user changes the content of the field:

<input type="text" size="30"
id="email" onchange="checkEmail()">;

onSubmit

The onSubmit event is used to validate ALL form fields before submitting it.

Below is an example of how to use the onSubmit event. The checkForm() function will be called when the user clicks the submit button in the form. If the field values are not accepted, the submit should be cancelled. The function checkForm() returns either true or false. If it returns true the form will be submitted, otherwise the submit will be cancelled:

<form method="post" action="xxx.htm"
onsubmit="return checkForm()">

onMouseOver and onMouseOut

onMouseOver and onMouseOut are often used to create "animated" buttons.

Below is an example of an onMouseOver event. An alert box appears when an onMouseOver event is detected:

<a href="http://www.w3schools.com"
onmouseover="alert('An onMouseOver event');return false">
<img src="w3schools.gif" width="100" height="30">
</a>

JavaScript的Try...Catch语句

The try...catch statement allows you to test a block of code for errors.

Examples

The try...catch statement
How to write a try...catch statement.

The try...catch statement with a confirm box
Another example of how to write a try...catch statement.

JavaScript - Catching Errors

When browsing Web pages on the internet, we all have seen a JavaScript alert box telling us there is a runtime error and asking "Do you wish to debug?". Error message like this may be useful for developers but not for users. When users see errors, they often leave the Web page.

This chapter will teach you how to trap and handle JavaScript error messages, so you don't lose your audience.

There are two ways of catching errors in a Web page:

By using the try...catch statement (available in IE5+, Mozilla 1.0, and Netscape 6)
By using the onerror event. This is the old standard solution to catch errors (available since Netscape 3)

Try...Catch Statement

The try...catch statement allows you to test a block of code for errors. The try block contains the code to be run, and the catch block contains the code to be executed if an error occurs.

Syntax

try
{
//Run some code here
}
catch(err)
{
//Handle errors here
}

Note that try...catch is written in lowercase letters. Using uppercase letters will generate a JavaScript error!

Example 1

The example below contains a script that is supposed to display the message "Welcome guest!" when you click on a button. However, there's a typo in the message() function. alert() is misspelled as adddlert(). A JavaScript error occurs:

<html>
<head>
<script type="text/javascript">
function message()
{
adddlert("Welcome guest!")
}
</script>
</head>
<body>
<input type="button" value="View message" onclick="message()" />
</body>
</html>

To take more appropriate action when an error occurs, you can add a try...catch statement.

The example below contains the "Welcome guest!" example rewritten to use the try...catch statement. Since alert() is misspelled, a JavaScript error occurs. However, this time, the catch block catches the error and executes a custom code to handle it. The code displays a custom error message informing the user what happened:

<html>
<head>
<script type="text/javascript">
var txt=""
function message()
{
try
  {
  adddlert("Welcome guest!")
  }
catch(err)
  {
  txt="There was an error on this page.nn"
  txt+="Error description: " + err.description + "nn"
  txt+="Click OK to continue.nn"
  alert(txt)
  }
}
</script>
</head>
<body>
<input type="button" value="View message" onclick="message()" />
</body>
</html>

Example 2

The next example uses a confirm box to display a custom message telling users they can click OK to continue viewing the page or click Cancel to go to the homepage. If the confirm method returns false, the user clicked Cancel, and the code redirects the user. If the confirm method returns true, the code does nothing:

<html>
<head>
<script type="text/javascript">
var txt=""
function message()
{
try
  {
  adddlert("Welcome guest!")
  }
catch(err)
  {
  txt="There was an error on this page.nn"
  txt+="Click OK to continue viewing this page,n"
  txt+="or Cancel to return to the home page.nn"
  if(!confirm(txt))
    {
    document.location.href="http://www.w3schools.com/"
    }
  }
}
</script>
</head> <body> <input type="button" value="View message" onclick="message()" /> </body> </html>

The onerror Event

The onerror event will be explained soon, but first you will learn how to use the throw statement to create an exception. The throw statement can be used together with the try...catch statement.

JavaScript的抛出语句

The throw statement allows you to create an exception.

Examples

The throw statement
How to use the throw statement.

The Throw Statement

The throw statement allows you to create an exception. If you use this statement together with the try...catch statement, you can control program flow and generate accurate error messages.

Syntax

throw(exception)

The exception can be a string, integer, Boolean or an object.

Note that throw is written in lowercase letters. Using uppercase letters will generate a JavaScript error!

Example 1

The example below determines the value of a variable called x. If the value of x is higher than 10 or lower than 0 we are going to throw an error. The error is then caught by the catch argument and the proper error message is displayed:

<html>
<body>
<script type="text/javascript">
var x=prompt("Enter a number between 0 and 10:","")
try
{ 
if(x>10) 
throw "Err1" 
else if(x<0)
throw "Err2"
} 
catch(er)
{
if(er=="Err1") 
alert("Error! The value is too high")
if(er == "Err2") 
alert("Error! The value is too low") 
}
</script>
</body>
</html>

JavaScript的onerror事件

在web页面中捕获错误的一个古老而通用的方法，就是使用onerror事件。

Examples

The onerror event (an example with an error)
How to use the onerror event to catch errors in a web page.

关于 onerror 事件

We have just explained how to use the try...catch statement to catch errors in a web page. Now we are going to explain how to use the onerror event for the same purpose.
我们刚刚介绍过如何通过try...catch语句捕获页面中的错误。现在我们再来看看如何通过onerror时间来达到同样的目的。

The onerror event is fired whenever there is a script error in the page.

To use the onerror event, you must create a function to handle the errors. Then you call the function with the onerror event handler. The event handler is called with three arguments: msg (error message), url (the url of the page that caused the error) and line (the line where the error occurred).
使用onerror事件前，我们需要一个用来处理错误的函数。当然你可以管这个函数叫onerror事件处理器。这个事件处理器调用三个参数：msg(错误消息),url(导致错误发生的页面url)和line(错误发生的代码所在行)

Syntax

onerror=handleErr function handleErr(msg,url,l) { //Handle the error here return true or false }

The value returned by onerror determines whether the browser displays a standard error message. If you return false, the browser displays the standard error message in the JavaScript console. If you return true, the browser does not display the standard error message.

Example

The following example shows how to catch the error with the onerror event:

<html>
<head>
<script type="text/javascript">
onerror=handleErr
var txt="" function handleErr(msg,url,l) { txt="There was an error on this page.nn" txt+="Error: " + msg + "n" txt+="URL: " + url + "n" txt+="Line: " + l + "nn" txt+="Click OK to continue.nn" alert(txt) return true } function message() { adddlert("Welcome guest!") } </script> </head> <body> <input type="button" value="View message" onclick="message()" /> </body> </html>

JavaScript中的特殊字符

在JavaScript中如果需要添加特殊字符，就需要在字符前加上反斜线。

Insert Special Characters
插入特殊字符

如果需要在字符串中增加换行、引号等特殊字符，需要在字符前增加反斜线（）

请看下面的JavaScript代码：

var txt="We are the so-called "Vikings" from the north."
document.write(txt)

In JavaScript, a string is started and stopped with either single or double quotes. This means that the string above will be chopped to: We are the so-called

To solve this problem, you must place a backslash () before each double quote in "Viking". This turns each double quote into a string literal:

var txt="We are the so-called "Vikings" from the north."
document.write(txt)

JavasScript will now output the proper text string: We are the so-called "Vikings" from the north.

Here is another example:

document.write ("You & me are singing!")

The example above will produce the following output:

You & me are singing!

The table below lists other special characters that can be added to a text string with the backslash sign:

Code	Outputs
'	single quote
"	double quote
&	ampersand
\	backslash
n	new line
r	carriage return
t	tab
b	backspace
f	form feed

JavaScript手册

Some other important things to know when scripting with JavaScript.
写JavaScript脚本时，还要知道些重要的东西

JavaScript是大小写敏感的

A function named "myfunction" is not the same as "myFunction" and a variable named "myVar" is not the same as "myvar".

JavaScript is case sensitive - therefore watch your capitalization closely when you create or call variables, objects and functions.

关于空格

JavaScript ignores extra spaces. You can add white space to your script to make it more readable. The following lines are equivalent:

name="Hege"
name = "Hege"

关于代码中的换行

You can break up a code line within a text string with a backslash. The example below will be displayed properly:

document.write("Hello 
World!")

However, you cannot break up a code line like this:

document.write 
("Hello World!")

关于注释

You can add comments to your script by using two slashes //:

//this is a comment
document.write("Hello World!")

or by using /* and */ (this creates a multi-line comment block):

/* This is a comment
block. It contains
several lines */
document.write("Hello World!")

订阅：博文 (Atom)