javascript - 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 = sumEl;
       sumEl.keyup(this.updateSumHandler);
    },

    updateSumHandler: function(event) {
       // Throws error here: "this.updateSum is not a function"
       this.updateSum();
    },

    updateSum: function() {
       // does something here
    }
});

How can I call this.updateSum() after all?

Answer 1

You need to use closures.

 initElements: function(sumEl) {
        this.sumEl = sumEl;
        var ref = this;
        sumEl.keyup( function(){ref.updateSumHandler();});
 },