为什么在IE8上b/w window.clearTimeout和clearTimeout有什么不同？

Question

我试图重写clearTimeout功能，在除了IE以外的浏览器上运行完全正常（在IE8测试）

clearTimeout = function(){}; 

IE8提供了以下错误：

Object doesn't support this action 

但是，当我这样做，

window.clearTimeout = function(){}; 

它可以很好的覆盖clearTimeout。这是为什么？

此外，无处不在我的代码我打电话clearTimeout而不是直接为window.clearTimeout。所以，即使我重写clearTimeout（通过第二种方式），本机clearTimeout被调用，而不是重写的clearTimeout。什么可以解决这个问题？

Answer 1

In IE, initially, the property setTimeout exists on the prototype of window, not on window itself. So, when you ask for window.setTimeout, it actually traverses one step on the prototype chain to resolve the reference. Similarly, when you ask for setTimeout, it traverses down the scope chain, then to window, then down the prototype chain to resolve the reference.

I suspect that IE has a built-in optimization where it automatically caches the resolution of implied globals that are discovered all the way down on the prototype of the global object. It would have good reason to do so, as these are commonly requested references, and traversing that chain is costly. However, it must be setting this reference as read-only, since it's just a caching optimization. This has the unfortunate side-effect of causing an exception to be thrown when attempting to assign to the reference by using it as an lvalue.

来源：http://www.adequatelygood.com/2011/4/Replacing-setTimeout-Globally