Question

I’m having some Javascript woes, lets say we have a constructor

function test(element) {
  this.element = element;
  this.element.onfocus = function() { this.onfocus(); }
}

test.prototype.onfocus = function() {
  alert("focused");
}

new test(document.getElementByID("E1"));

So I am trying to dynamically set the focus event inside the constructor, but it doesn’t seem to work, and I can’t figure it out.

Anyone help?

Thanks,

AJ

Answer 1

In JavaScript, and in the context of this.element.onfocus = function() {this.onfocus(); }, second this is the element who fired the event.

In other words, your code should be like this if you want to work in a proper way:

function test(element) {
  this.element = element;

  var currentObject = this;
  this.element.onfocus = function() {currentObject.onfocus(); }
}

Don’t think JavaScript is a decent object-oriented programming language, as it’s prototype-oriented and it has some weak things like one that’s affecting your code.

Why don’t you read this article? I belive it’ll clarify this keyword for you:

• http://www.switchonthecode.com/tutorials/javascript-tutorial-why-the-this-keyword-breaks