使用Greasemonkey访问Javascript私有变量

Question

function Foo1() {
    var bar = 'test';
}

AFAIK, it is impossible to access the variable bar from global scope, unless one writes a privileged function to do so, such as

function Foo2() {
    var bar = 'test';
    this.read = function(){return bar;};
}

Does Greasemonkey (or any other tool) provide any means to access the variable bar, short of re-defining the entire function Foo1 with Foo2? Greasemonkey has GM_xmlhttprequest which sidesteps certain restrictions, so I was wondering if it could do this too and save me some issues.

What I am trying to do currently is to read and write a private variable embedded in a function, which is also itself located in a separate .js include. Thus, I cannot directly modify the script, and I have to load the .js with AJAX, carry out the modification, and then overwrite the original script. This is very cumbersome and I would like an easier way to carry this task out.

Answer 1

GM_xmlhttprequest just bypasses browser security. Variable scope, on the other hand, is part of the language and the Javascript VM. Short of modifying the Javascript VM, there is no way to access those 'private' variables outside the function scope.

Answer 2

If Foo1 is not a native function and you do know the pattern of the function, then you can get the content of the variable by using:

var bar = /bar = '(\w+)'/.test(Foo1.toString()) && RegExp.$1;
alert(bar); // will return "test"