像C++一样写JavaScript
C/C++/Java的include或import可以引用第3方文件和包. 这个功能在Html/Js里没有默认的实现. 假设我们有这样一个HTML文件index.html:
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd"> <html xmlns="http://www.w3.org/1999/xhtml"> <head id="Head1"> <title>欢迎使用ligerUI</title> <link href="lib/ligerUI/skins/Aqua/css/ligerui-all.css" rel="stylesheet" type="text/css" /> <link href="lib/ligerUI/skins/Gray/css/all.css" rel="stylesheet" type="text/css" /> <link href="lib/css/common.css" rel="stylesheet" type="text/css" /> <link href="lib/css/index.css" rel="stylesheet" type="text/css" /> <script src="lib/jquery/jquery-1.5.2.min.js" type="text/javascript"></script> <script src="lib/ligerUI/js/ligerui.min.js" type="text/javascript"></script> <script src="lib/ligerUI/js/plugins/ligerTab.js" type="text/javascript"></script> <script src="lib/ligerUI/js/plugins/ligerLayout.js" type="text/javascript"></script> <script src="lib/js/common.js" type="text/javascript"></script> <script src="lib/js/LG.js" type="text/javascript"></script> <script src="lib/js/login.js" type="text/javascript"></script> <script src="/lib/jquery-validation/jquery.validate.min.js" type="text/javascript"></script> <script src="/lib/jquery-validation/jquery.metadata.js" type="text/javascript"></script> <script src="/lib/jquery-validation/messages_cn.js" type="text/javascript"></script> <script src="lib/js/changepassword.js" type="text/javascript"></script> <script src="lib/ligerUI/js/plugins/ligerForm.js" type="text/javascript"></script> <!-- settings menus --> <script src="index.html.js" type="text/javascript"></script> </head> <body> ... </body> </html>
可以看到, 为了使用某个第3方库(这里是ligerUI), 我们不得不把所有需要的js文件在html里引入进来. 下面修改上面的index.html, 看看新的写法可以给我们带来什么惊喜:
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
<html xmlns="http://www.w3.org/1999/xhtml">
<head id="Head1">
<title>欢迎使用ligerUI</title>
<link href="lib/ligerUI/skins/Aqua/css/ligerui-all.css" rel="stylesheet" type="text/css" />
<link href="lib/ligerUI/skins/Gray/css/all.css" rel="stylesheet" type="text/css" />
<link href="lib/css/common.css" rel="stylesheet" type="text/css" />
<link href="lib/css/index.css" rel="stylesheet" type="text/css" />
<script src="lib/prerequisite.js" type="text/javascript"></script>
<script src="index.html.js" type="text/javascript"></script>
</head>
<body>
...
</body>
</html>
是不是简洁多了, 这个写法的关键是我们必须在引用任何js之前引入一个全局的API文件, 这里是prerequisite.js, 然后就可以引入自己的js文件, 这里是index.html.js, 在自己的js文件里引入所有我们需要的第3方库文件(如ligerUI). 下面我们看看index.html.js这个文件里作了什么:
/**
* index.html.js
* version: 0.0.1
*/
UTIL.importScripts(
"lib/jquery/jquery-1.5.2.min.js",
"lib/ligerUI/js/ligerui.min.js",
"lib/js/common.js",
"lib/js/LG.js",
"lib/js/login.js",
"lib/jquery-validation/jquery.validate.min.js",
"lib/jquery-validation/jquery.metadata.js",
"lib/jquery-validation/messages_cn.js",
"lib/js/changepassword.js"
);
/* 下面是业务代码, 和文件包含没关系 */
(function (window, undefined) {
"use strict";
/**
* public interfaces
*/
}(window));
是不是很神奇呢, 这个和C/C++/java很像啦. UTIL.importScripts(...) 这个函数帮我们做了一切事情, 它是在 prerequisite.js 中定义的, 那么最后就是prerequisite.js文件:
/**
* prerequisite.js
* included before all *.js
* version: 0.0.1
* cheungmine
* 2012-5
*/
(function (window, undefined) {
"use strict";
window.UTIL = {}
/* Modify DEBUG = false if release */
var DEBUG = true;
var log = function () {
if (window.UTIL.DEBUG === true) {
/* Thanks to Paul Irish for this one:
* http://paulirish.com/2009/log-a-lightweight-wrapper-for-consolelog/
*/
log.history = log.history || [];
log.history.push(arguments);
/* Make sure console is present */
if ('object' === typeof console) {
/* Setup console and arguments */
var c = console[console.warn? 'warn':'log'],
args = Array.prototype.slice.call(arguments),
a;
/* Add marker to first argument if it's a string */
if (typeof arguments[0] === 'string') {
/* args[0] = 'your marker: ' + args[0]; */
}
/* Apply console.warn or .log if not supported */
a = c.apply? c.apply(console, args) : c(args);
}
}
};
var getScriptPath = function (jsfile) {
var e = {};
var htmlPath = "";
var jsPath = "";
if (document.location.protocol === 'file:'){
e.BasePath = unescape(document.location.pathname.substr(1));
e.BasePath = 'file://' + e.BasePath.substring(0,e.BasePath.lastIndexOf('/')+1);
e.FullBasePath = e.BasePath;
} else {
e.BasePath = document.location.pathname.substring(0,document.location.pathname.lastIndexOf('/')+1);
e.FullBasePath = document.location.protocol + '//' + document.location.host + e.BasePath;
}
htmlPath = e.FullBasePath;
var i, at, src, slc, scriptTag = document.getElementsByTagName("script");
for (i = 0; i < scriptTag.length; i++) {
src = scriptTag[i].src;
at = src.lastIndexOf(jsfile);
if (at!==-1) {
at++;
slc=src.toLowerCase();
if (slc.indexOf("file://") === 0) {
jsPath = src.substring(0,at);
break;
} else if (slc.indexOf("http://") === 0) {
jsPath = src.substring(0,at);
break;
} else if (slc.indexOf("https://") === 0) {
jsPath = src.substring(0,at);
break;
} else if (slc.indexOf("../") === 0) {
jsPath = htmlPath + src.substring(0,at);
break;
} else if (slc.indexOf("./") === 0) {
jsPath = htmlPath + src.substring(0,at);
break;
} else if (slc.indexOf("/") === 0) {
if (document.location.protocol === 'http:' || document.location.protocol === 'https:') {
jsPath = document.location.protocol + "//" + document.location.host + src.substring(0,at);
}
break;
} else if (slc.search(/^([a-z]{1}):/) >= 0) {
jsPath = src.substring(0,at);
break;
} else {
jsPath = htmlPath;
}
}
}
return jsPath;
};
var getScriptName = function () {
var js = document.scripts;
return js[js.length-1].src.substring(js[js.length-1].src.lastIndexOf("/"));
}
var appendScript = function (url, source, head) {
if ( source && !document.getElementById(url) ) {
var oHead = head ? head : document.getElementsByTagName("HEAD").item(0);
var oScript = document.createElement("script");
oScript.language = "javascript";
oScript.type = "text/javascript";
oScript.id = url;
oScript.defer = true;
oScript.text = source;
oHead.appendChild(oScript);
}
}
var importScripts = (function (globalEval) {
var oHead = document.getElementsByTagName("HEAD").item(0);
var xhr = null;
if (window.XMLHttpRequest) {
xhr = new XMLHttpRequest();
} else if ( window.ActiveXObject ) {
try {
xhr = new ActiveXObject("MsXml2.XmlHttp");
} catch (e) {
xhr = new ActiveXObject("Microsoft.XMLHTTP");
}
}
if (! xhr) {
throw "prerequisite.js: XMLHttpRequest Not supported."
}
var basePath = null;
return function importScripts () {
var
args = Array.prototype.slice.call(arguments),
len = args.length,
i = 0,
meta,
data,
content
;
if (!basePath) {
basePath = getScriptPath(getScriptName());
}
for (; i<len; i++) {
var url = basePath + args[i];
if (url.substr(0, 5).toLowerCase() === "data:") {
data = url;
content = data.indexOf(",");
meta = data.substr(5,content).toLowerCase();
data = decodeURIComponent(data.substr(content+1));
if (/;s*base64s*[;,]/.test(meta)) {
data=atob(data);
}
if (/;s*charset=[uU][tT][fF]-?8s*[;,]/.test(meta)) {
data = decodeURIComponent(escape(data));
}
} else {
xhr.open("GET", url, false /* async = false */);
xhr.send(null);
data = xhr.responseText;
}
/* globalEval(data); */
appendScript(url, data, oHead);
}
};
} (eval));
/**
* global functions:
*/
window.UTIL.ERRINDEX = -1;
window.UTIL.DEBUG = DEBUG;
window.UTIL.log = log;
window.UTIL.importScripts = importScripts;
}(window));
最后我总结一下, 为了实现类似C/java的文件引用包含, 我写了一个prerequisite.js, 它提供全局的函数UTIL.importScripts(), prerequisite.js唯一的要求就是必须在页面的其他js加载前加载. 以后我们就可以在我们的js里使用UTIL.importScripts() 包含任何你想要包含的js文件. 因为我们必须要保证包含的文件必须被加载, 因此UTIL.importScripts()采用的是同步模式.
好了, 大胆的使用这个技巧吧, 你就可以实现真正的code behind. 总共就3步:
1) 写一个A.html, 并将prerequisite.js作为第一个引入的js文件;
2) 写自己的B.js库, 需要引用其他C.js, D.js, E.js文件的时候,就在B.js文件头部使用
UTIL.importScripts("/path/C.js", "/path/D.js", "/path/E.js");
3) path是C,D,E.js相对于B.js的路径.