【转】js 关于new的讨论

一直不清楚new到底是怎么样的操作
看了winter那个理解面向对象总算有些明白
为了弄清楚ecma这个天书现在也得啃了
winter说new其实就是调用 [[Construct]]
13.2.2 [[Construct]]
When the [[Construct]] property for a Function object F is called, the following steps are taken:
1.        Create a new native ECMAScript. object.
2.        Set the [[Class]] property of Result(1) to "Object".
3.        Get the value of the prototype property of the F.
4.        If Result(3) is an object, set the [[Prototype]] property of Result(1) to Result(3).
5.        If Result(3) is not an object, set the [[Prototype]] property of Result(1) to the original Object prototype object as described in section 15.2.3.1.
6.        Invoke the [[Call]] property of F, providing Result(1) as the this value and providing the argument list passed into [[Construct]] as the argument values.
7.        If Type(Result(6)) is Object then return Result(6).
8.        Return Result(1).

下面是我的理解
例如 f = new F
1 2大概可以理解成是建一个对象
x = {}
3 是
p = F.prototype
4 如果p是object就
x.[[Prototype]] = p
5 如果p不是object就
x.[[Prototype]] = Object.prototype
6 运行F.[[Call]]（就是调用F）， 并以x作为this，还有参数
7 如果6的结果的是对象，就返回6的结果
8 否则返回x（通常情况）

abcdreamer发布于2009-05-30 17:58:46

不错。
函数比对象多的，应该就是prototype、[[Construct]]、[[Call]]。
[[Call]]使函数可以执行，prototype和[[Construct]]为new服务，使可以创建实例。

abcdreamer发布于2009-05-30 18:05:27

CODE:

<script>
function f() {}
alert(new f().constructor);
f.prototype = f;
alert(new f().constructor);
delete f.prototype;
alert(new f().constructor);
</script>

dh20156发布于2009-05-31 12:56:50

CODE:

<script type="text/javascript">

/*
   new操作原理（spiderMonkey引擎下）
*/

var a = function(sA,sH){
    var x = "x";
    this.a = sA;
    this.h = sH;
    this.say = function(){alert(this.a+','+x)}
}
a.prototype.hi = function(){alert(this.h)}

var createInstance = function(source){
    var p = {}
    var args = Array.prototype.slice.call(arguments,1);
    source.apply(p,args);
    p.__proto__ = source.prototype;
    return p;
}

var A = createInstance(a,"A","hi A");
A.say();
A.hi();

</script>

abcdreamer发布于2009-05-31 13:00:20

我记得是先关联prototype，然后执行构造函数啊

CODE:

<script>
function f() {
  alert(this.a);
}
f.prototype.a = 1;
new f;
</script>