http://crockford.com/javascript/jsmin
JSMin
the javascript minifier
douglas crockford
www.crockform.com
2003-12-04
JSMin是一个过滤器,他能够移除js文件所有的注释和不需要的空行.他能够把js文件压缩到原来的一半左右,好吃就是能够很快的被下载到本地,它同时提倡一种更好看的编程风格,去除了那些不需要的东西.
JSMin做了些什么:
JSMin就是一个过滤器,他能够忽略并修改一些字符,当不改变程序的逻辑的情况下最小化js文件,可能这样做的结果是很难去debug,并且不容易阅读.
JSMin首先会将回车符合(carriage returns)替换为换行(linefeeds),同时把其他的所有的控制字符替换为一个空格,然后把单行注释(//)替换为一个换行.把多行注释替换为空格,多个空格会被替换为一个空格,多个换行会被替换为一个换行,
它会忽略空格,除非空格是一个非ascii编码的字节,或者一个ascii的字母或者数字,
或者下面的几个字符:
￥ $ _
通常他对于处理换行的情况比较谨慎,因为会起到分号的作用.如果一个换行符它是非ascii字节,或者是一个ascii字母或者数字,或者下面的几个字符:
\ $ _ { [ ( + –
这个时候是不会被忽略的.
and if it follows a non-ASCII character or an ASCII letter or digit or one of these characters:
\ $ _ } ] ) + – ” ‘
No other characters are omitted or modified.
JSMin knows to not modify quoted strings and regular expression literals.
JSMin does not obfuscate, but it does uglify.
Before:
// is.js
// (c) 2001 Douglas Crockford
// 2001 June 3
// is
// The -is- object is used to identify the browser. Every browser edition
// identifies itself, but there is no standard way of doing it, and some of
// the identification is deceptive. This is because the authors of web
// browsers are liars. For example, Microsoft’s IE browsers claim to be
// Mozilla 4. Netscape 6 claims to be version 5.
var is = {
ie: navigator.appName ‘Microsoft Internet Explorer’,
java: navigator.javaEnabled(),
ns: navigator.appName ‘Netscape’,
ua: navigator.userAgent.toLowerCase(),
version: parseFloat(navigator.appVersion.substr(21)) ||
parseFloat(navigator.appVersion),
win: navigator.platform ‘Win32′
}
is.mac = is.ua.indexOf(‘mac’) >= 0;
if (is.ua.indexOf(‘opera’) >= 0) {
is.ie = is.ns = false;
is.opera = true;
}
if (is.ua.indexOf(‘gecko’) >= 0) {
is.ie = is.ns = false;
is.gecko = true;
}
After:
var is={ie:navigator.appName’Microsoft Internet Explorer’,java:navigator.javaEnabled(),ns:navigator.appName’Netscape’,ua:navigator.userAgent.toLowerCase(),version:parseFloat(navigator.appVersion.substr(21))||parseFloat(navigator.appVersion),win:navigator.platform’Win32′}
is.mac=is.ua.indexOf(‘mac’)>=0;if(is.ua.indexOf(‘opera’)>=0){is.ie=is.ns=false;is.opera=true;}
if(is.ua.indexOf(‘gecko’)>=0){is.ie=is.ns=false;is.gecko=true;}
字符编码:
jsmin需要但是并不会去验证输入到程序里的字符编码格式,ascii和utf-8都是可以的,但是不保证其他的编码格式也是正确的.
注意:
确保备份你的原文件,因为jsmin不会给你提供一个撤销的功能.
Do not put raw control characters inside a quoted string. That is an extremely bad practice. Use \xhh notation instead. JSMin will replace control characters with spaces or linefeeds.
使用括号来区别混乱的序列,举例,最小化想把
a + ++b
改为
a+++b
当时会被改成这样子:
a++ + b
这个时候就需要括号来清楚地区分顺序:
a + (++b)
JSLint(http://www.jslint.com/)) checks for all of these problems. It is suggested that JSLint be used before using JSMin.
建议在使用jsmin之前使用jslint来检测代码质量
命令行选项:
Optional parameters will be listed at the beginning of the output as comments.
This is a convenient way of replacing copyright messages and other documentation.
Example:
jsmin
Errors
JSMin can produce three error messages to stderr:
Unterminated comment.
Unterminated string constant.
Unterminated regular expression.
It ignores all other errors that may be present in your source program.
—
一些有用的地址:
http://www.yuiblog.com/blog/
http://coderjournal.com/
http://developer.yahoo.com/
http://yuiblog.com/blog/2006/03/06/minification-v-obfuscation/
http://www.julienlecomte.net/blog/2007/08/11/
http://dojotoolkit.org/
http://dean.edwards.name/packer/
http://compressorrater.thruhere.net/
http://en.wikipedia.org/wiki/Http_compression