嵌套函数中的变量“未定义”

Question

windows.onload=function(){
    ...somecode...
    var scene = new THREE.Scene();
    ...somecode...
    var i;
    var j;
    for (i=......){...}
    func2();
    function func2(){
        ...somecode...
        BREAK AT THIS LINE;
    }
}

when I break at that line,
firebug says, "i" and "j" is undefined,but an inner function obviously can get the value of "i" right?
but weirdly, "scene" is showed correctly.
the Ctrl+Shift+I of chrome shows the same thing.

but the thing more weird is, when I add

alert(i);

to the beginning of func2,
this time, the msgBox tells the value of i correctly,
firebug shows the value of i correctly,
but j is still showed undefined.

I'm wondering why,
Both Firebug and chrome shows the same thing so it seems not a bug of Firebug,
so is there any hints for this?

thanks a lot.

Answer 1

The value of i should be available in the inner function. This prints "2" in Firebug and node.js as expected:

(function() { 
     for (var i=0; i<2; ++i) {}; 
     (function() { console.log(i) })(); 
})();

So is it just a matter of the debugger showing incorrect values?

Answer 2

function func2(){
    BREAK HERE;
    ...
    for (var i = ...
    for (var j = ...
}

If you have code like that then those var statements get hoisted to the top of the function declaration so it actually looks like

function func2() {
    var i, j;
    BREAK HERE:
    ...
    for (i = ...
    for (j = ...
}

Other then that, there is no reason for i and j to be undefined