JavaScript, MooTools - Variable scope in Class/overwrite global variable

Can somebody explain me, why I am开发者_开发问答 able to overwrite a method value of a global instance by just setting its value locally and why I am not able to do something similar with variables?

Is the only way to access the variable to use the window object hierarchy? Or is there maybe a shorter way?

(function() {
    console.log(this);

    var someVar = this.someVar = false;

    var subClass = new Class({
        test: false,

        setValue: function(value) {
            this.test = value
        }
    });

    var subPub = this.subPub = new subClass();

    var MainClass = new Class({
        rewriteVar: function() {
            console.log("someVar = " + someVar); // returns global value
            console.log("subPub.test = " + subPub.test); // returns global value

            someVar = true;

            console.log("someVar local: " + someVar); // returns new local value
            console.log("someVar global: " + window.someVar); // returns old global value

            subPub.setValue(true);

            console.log("subPub.test local: " + subPub.test); // returns new local value
            console.log("subPub.test global: " + window.subPub.test) // returns new global value
        }
    });

    /* var someObj = this.someObj = {};

    var someVar = someObj.someMeth = false;

    // And why is this possible?
        var MainClass = new Class({
            rewriteVar: function() {
            someObj.someMeth = true;
            console.log(window.someObj.someMeth); // returns new global value
        }
    }); */

    window.addEvent("load", function() {
        var test = new MainClass();
        test.rewriteVar()
    })
})()

This is to do with variable scope. Javascript has functional scope.

So by doing:

var someVar = this.someVar = false;

You are declaring a local variable someVar and a global variable (which gets hoisted to the window object ie window.someVar), as this within your closure referes to the global scope ie window.

So when you write:

someVar = true;

You are overwriting the local variable with this new value.

Variables declared within a function definition are local to that function if you use the var key word:

(function () {
   var name = 'Mark';
})();
// Out here you cannot access name
console.log(name);

(if i understood correctly the problem)

It has nothing to do with Mootools or the clases, @Felix_Kling already gave you the answer but I will ilustrate it with a simple example:

var aObj = bObj = {}; //since bObj is an 'object', aObj will store the objects reference 
aObj.foo = "bar";
console.log(aObj.foo);
console.log(bObj.foo);
// output:
//     "bar"
//     "bar"


var a = b = 1; //since 'b' is primitive, 'a' will not store a reference of 'b', it will only copy it's value
a = 0;
console.log(a);
console.log(b);
// output:
//     0
//     1

i'm not really sure if this is what you were asking =) Hope this helps