为什么迭代窗口对象的属性会导致IE错误？

Question

I experiences this problem very often and finally thought that it might be worth a question here.

Running the following code in IE, results in the output frameElement , which means, that the property frameElement was found but if you try to access it via window["frameElement"] it throws an error.

for (var i in window){
    try {
        var c = window[i]
    } catch(e) {
        console.log(i);
    }
}

FIDDLE

I originally realized this problem when i tried to simply access every property of window, but always ended up with an error.

Does anyone know the reason for this? How can it be, that there is a property but that it is not accessible?

Answer 1

This can happen on any browser. Properties on any object, including Window, can be getters methods that can have side-effects including throwing exceptions.