像C++一样写JavaScript

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*base64\s*[;,]/.test(meta)) {
                        data=atob(data);
                    }

                    if (/;\s*charset=[uU][tT][fF]-?8\s*[;,]/.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.








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