问题
I'd believed that all global variables were accessible from the global object. So if I can access x (and x isn't bound locally), then window.x is the same value.
However, in a webpage (on JSFiddle):
window === this // true in Chrome and Firefox
toString === window.toString // true in Chrome and Firefox
But in the console:
window === this // true in Chrome console and Firebug, false in Firefox web console
toString === window.toString // false in Chrome, Firebug and Firefox web console
Why is this? Why is window the global object in Chrome's console but toString not bound to window.toString? What is toString bound to in Firefox's console? What other global values are different in the console?
回答1:
toString is not a global variable. It's a method shared by almost all objects, including the window object.
An actual global variable would always be available on the window object.
回答2:
perhaps this is related to this question? It's all related to the context, I believe
toString.call("foo") == this.toString.call("foo")
but
tostring.call("foot") != window.toString.call("foo") when this != window
回答3:
I cannot reproduce your claim in Firefox. They're both returning [xpconnect wrapped native prototype].
To help clear this up: everything available globally IS available via the global object. However, there could be properties available through the global object that are not necessarily available globally. This is due to the prototypal inheritance pattern in Javascript and the lack of specification on how this situation should be handled.
So, should an interpreter attempt to resolve global lookups via prototypal inheritance down the global object chain? Does the global object inherit from anything else? I think the various Javascript interpreters are inconsistent here, but someone more familiar with ECMAScript specifications could weigh in.
来源：https://stackoverflow.com/questions/14160211/why-isnt-tostring-equivalent-to-window-tostring