Sett scope on javascript function call

I want to call a javascript function within a protected scope and i can do it this way

var a = "Global a";
( function() {
    var a = "Local a";
    var alertA = function() {
      alert(a);
    }
    alertA(); 
})();

This alerts "Local a" butt what i realy would like to do is to get the same result with an already declared function.

var a = "Global开发者_如何转开发 a";
var alertA = function() {
    alert(a);
}

( function() {
    var a = "Local a";
    alertA(); 
})();

So my question is how can a call alertA with a different scope so the result would be "Local a"

The reason i would like to do this i want to call globally defined functions on different iframes and have global variabels like document and window point to the appropriate documents and windows for every specific iframe.

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Let me put it as an answer:

I suggest you make the function accept window and document as argument:

function someFunc(window, document, otherParameter) {

}

In each frame, you can then take its window and document as pass it to the function. For convenience, you can create a wrapper function in each frame, which does this for you:

var localSomeFun = function() {
    return someFun.apply(null, [window, document].concat(arguments));
}

---

use the following:

var a = "Global a";
var alertA = function () {
    alert(a);
}

(function () {
    var a = "Local a";
    alertA.apply(window, []);
})();

---

I guess you will have to refactor your code a bit, I enclose my solution:

var a = "Global a",
    alertA = function() {
        console.log(this.a);
    };

alertA();

(function() {
    var context = {};

    context.a = "Local a";

    alertA.call(context);
})();

You will have to store all variables in a specialized context object. Inside a function you will need to use this.%variable_name% instead of plain %variable_name%.