Overwritten “this” variable problem or how to call a member function?

Question

I have this class where I am using a combination of jQuery and Prototype:

var MyClass = Class.create({
    initElements: function(sumEl) {
       this.sumEl          


        

Answer 1

It is the famous Javascript idiom you need to use in initElements function:

var that = this;

Later in your handler just refer to that instead of this:

var MyClass = Class.create({
    initElements: function(sumEl) {
        this.sumEl = sumEl;
        var that = this;
        sumEl.keyup(this.updateSumHandler);
    },
    updateSumHandler: function(event) {
        that.updateSum();
    },
    updateSum: function() {
        // does something here
    }
});

It was covered in great detail in talk by Stuart Langridge on Javascript closures at Fronteers 2008 conference.