loadScript,非阻塞 JavaScript 加载库

快来打我* 2022-08-20 08:18 131阅读 0赞

在看高性能JavaScript书的时候看到一个写法，当然现在很多库了（when.js等），然后取github上收了下，算是它的一个封装。

地址：[https://github.com/marcbuils/jquery.loadscript/blob/master/jquery.loadscript.js][https_github.com_marcbuils_jquery.loadscript_blob_master_jquery.loadscript.js]

/**
     * PluginAutoLoad: Load your plugins on html DOM without javascript code.
     * http://marcbuils.github.com/jquery.pluginautoload/
     * https://github.com/leiming/jquery.loadscript
     *
     * Par Marc Buils ( marc.buils@marcbuils.fr )
     * Lei Ming ( poetcoders@gmail.com )
     * Sous licence LGPL v3 (http://www.gnu.org/licenses/lgpl-3.0.txt)
     *
     * v0.1.1 - 09/16/2015:
     * First release
     *
     * v0.1.2 - 12/09/2015;
     * Fix lazyLoad bug
     */
    
    $(function () {
      // lazyload script
      // ref: http://www.nczonline.net/blog/2009/07/28/the-best-way-to-load-external-javascript/
      // https://developer.mozilla.org/en-US/docs/Web/API/HTMLScriptElement
      var _loadScript = function (url, params, callback) {
    
        var script = document.createElement("script");
        script.type = "text/javascript";
    
        if (script.readyState) { //IE
          script.onreadystatechange = function () {
            if (script.readyState == "loaded" || script.readyState == "complete") {
              script.onreadystatechange = null;
              callback();
            }
          };
        } else { //Others
          script.onload = function () {
            callback();
          };
        }
    
        var scriptsProperties = [
          'type', 'src', 'htmlFor', 'event', 'charset', 'async', 'defer', 'crossOrigin', 'text', 'onerror'
        ];
    
        if (typeof params === 'object' && !$.isEmptyObject(params)) {
          for (var key in params) {
            if (params.hasOwnProperty(key) && $.inArray(key, scriptsProperties)) {
              script[key] = params[key];
            }
          }
        }
    
        document.getElementsByTagName(params['lazyLoad'] ? 'body' : 'head')[0].appendChild(script);
        script.src = url;
      };
    
      $.loadScript = function (p_url, p_params, p_callback) {
    
        // Handle p_params is exist
        if (arguments.length === 2 && typeof arguments[1] === 'function') {
          p_callback = arguments[1];
          p_params = {}
        }
    
        p_params = p_params || {};
    
        var _return = $.Deferred();
    
        // Call callback if necessary
        if (typeof( p_callback ) === 'function') {
          _return.done(function () {
            p_callback();
          });
        }
    
        // Load javascript file
        _loadScript(p_url, p_params, function () {
          _return.resolve();
        });
    
        return _return.promise();
      };
    })

具体看： [https://github.com/marcbuils/jquery.loadscript][https_github.com_marcbuils_jquery.loadscript]

关于script标签属性，可以看看这里[HTMLScriptElement][]，[https://developer.mozilla.org/zh-CN/docs/Web/API][https_developer.mozilla.org_zh-CN_docs_Web_API]  
另3篇：

第一个[loadScript][]可以看看 [https://github.com/zynga/loadScript/blob/master/loadScript.js][https_github.com_zynga_loadScript_blob_master_loadScript.js]

第二个是雅虎的LazyLoad，[**https://github.com/rgrove/lazyload/blob/master/lazyload.js**][https_github.com_rgrove_lazyload_blob_master_lazyload.js]

LazyLoad 是一个更强大的 loadScript()函数。 LazyLoad 精缩之后只有大  
约 1.5KB（精缩，而不是用 gzip 压缩的）。用法举例如下：

// Load a single JavaScript file and execute a callback when it finishes.
    LazyLoad.js('http://example.com/foo.js', function () {
      alert('foo.js has been loaded');
    });
    
    // Load multiple JS files and execute a callback when they've all finished.
    LazyLoad.js(['foo.js', 'bar.js', 'baz.js'], function () {
      alert('all files have been loaded');
    });
    
    // Load a CSS file and pass an argument to the callback function.
    LazyLoad.css('foo.css', function (arg) {
      alert(arg);
    }, 'foo.css has been loaded');
    
    // Load a CSS file and execute the callback in a different scope.
    LazyLoad.css('foo.css', function () {
      alert(this.foo); // displays 'bar'
    }, null, {foo: 'bar'});

第三个非阻塞 JavaScript 加载库是 LABjs：[https://github.com/getify/LABjs][https_github.com_getify_LABjs]，此库对加载过程进行更精细的控制，并尝试并行下载尽可能多的代码。具体可以看

它的官网（http://labjs.com/documentation.php）或者github。

[https_github.com_marcbuils_jquery.loadscript_blob_master_jquery.loadscript.js]: https://github.com/marcbuils/jquery.loadscript/blob/master/jquery.loadscript.js
[https_github.com_marcbuils_jquery.loadscript]: https://github.com/marcbuils/jquery.loadscript
[HTMLScriptElement]: https://developer.mozilla.org/en-US/docs/Web/API/HTMLScriptElement
[https_developer.mozilla.org_zh-CN_docs_Web_API]: https://developer.mozilla.org/zh-CN/docs/Web/API
[loadScript]: https://github.com/zynga/loadScript
[https_github.com_zynga_loadScript_blob_master_loadScript.js]: https://github.com/zynga/loadScript/blob/master/loadScript.js
[https_github.com_rgrove_lazyload_blob_master_lazyload.js]: https://github.com/rgrove/lazyload/blob/master/lazyload.js
[https_github.com_getify_LABjs]: https://github.com/getify/LABjs