Assign object to “this”

Question

Say I have a class and some static helper methods like this:

function MyClass (myVar) {
    this.myVar = myVar;

    this.replaceMe = function (value) {
             


        

Answer 1

I wanted to do something very similar a while back. Unfortunately there's no way to assign a value to this - the this pointer is a read only variable. However the next best thing is to use a getter and setter object to change the variable holding your instance itself.

Note that this only updates a single reference to the instance. You can read more about it here: Is there a better way to simulate pointers in JavaScript?

So this is how it works:

function MyClass(pointer, myVar) {
    this.myVar = myVar;

    this.replaceMe = function (value) {
        pointer.value = MyClass.staticHelper(this, pointer, value);
        return pointer.value;
    };

    this.revealVar = function () {
        alert(this.myVar);
    };
}

MyClass.staticHelper = function (instance, pointer, value) {
    return new MyClass(pointer, instance.myVar + value);
};

This is how to create the pointer and use it:

var instance = new MyClass({
    get value() { return instance; },
    set value(newValue) { instance = newValue; }
}, 2);

instance.revealVar();               // alerts 2
instance.replaceMe(40).revealVar(); // alerts 42

It's not the most elegant solution but it gets the job done. You can see this code in action: http://jsfiddle.net/fpxXL/1/