swfupload 源码翻阅笔记二 _Web前端

swfupload 源码阅读笔记二

SWFUpload.prototype.initSWFUpload = function (settings) {
        try {
                this.customSettings = {};       // A container where developers can place their own settings associated with this instance.
                this.settings = settings;
                this.eventQueue = [];
                this.movieName = "SWFUpload_" + SWFUpload.movieCount++;
                this.movieElement = null;
        // 略

注意：

SWFUpload.movieCount 是在 SWFUpload.prototype.initSWFUpload 语句之后定义的，

SWFUpload.movieCount = 0;

也就是说，要么，prototype.initSWFUpload 只是注册声明的作用，并没有被执行；要么，静态成员的初始化要先于对象成员的初始化。

做一个实验：

<html>
        <head>
                <script type="text/javascript">
                        //var a = 2;
                        var a;
                        if (a === undefined) {
                                alert("a is undefined.");
                                a = function(){this.initA();};
                                alert(a);
                        } else {
                                alert("a is defined.");
                        }
                
                        a.prototype.initA = function () {
                                this.count = ++a.start;
                                alert("initA: a = " + this.count); 
                        };
                        alert("before assignment of a.start");
                        a.start = 0;
                        var b = new a();
                        
                </script>
        </head>
        <body>
                
        </body>
</html>

执行结果是：

a is undefined.

function () {
??? this.initA();
}

before assignment of a.start

initA: a = 1

这个只是验证了 “prototype.initSWFUpload 只是注册声明的作用，并没有被执行”。同时说明 a = function(){this.initA();}; 只是定义了 a 这个类，而不是真正的初始化；只有 var b = new a(); 才是真正的初始化。

将 a.start = 0; 替换到 var b = new a(); 后面，则显示

initA: a = NaN

所以静态成员必须人为地放到相关的 public 对象的初始化之前。

// ---------------------------------------

补充参考，关于javascript 类定义中，private, privileged, public, static member 的实现：

http://robertnyman.com/2008/10/14/javascript-how-to-get-private-privileged-public-and-static-members-properties-and-methods/

1 楼三尺寒冰 2011-07-20

深刻呀。。。。