Using 'this' inside a link generated by a javascript object

Question

Javascript is pretty shaky for me, and I can't seem to find the answer to this. I have some code along the lines of

var Scheduler = function(divid,startDate,mode){

    this.setHeader = function(){
          header.innerHTML = '<a href="#" onclick="this.showScheduler(1);">Show</a>';

    }

   this.showScheduler = function period(){

        ...
   }

};

My problem is, how do I put the onclick into the HTML so that it properly calls the showScheduler function for the appropriate instance of the current scheduler object that I'm working with?

Answer 1

I wouldn't do whatever it is you're doing the way you're doing it, but with the code the way you have it, I would do this (lots ofdo and doing :) ):

var Scheduler = function(divid, startDate, mode){
    var that = this;

    this.setHeader = function(){
          header.innerHTML = '<a href="#">Show</a>';
          header.firstChild.onclick = function() { that.showScheduler(1); };
    }

   this.showScheduler = function period(){

        ...
   }
};

Answer 2

You should use a framework for this type of thing. If you don't use one then you gotta declare each instance of schedular as a global object, and you will need the name of the instance in order to call it from the link. Look at the following link

http://developer.yahoo.com/yui/examples/event/eventsimple.html

They only show a function being applied, but you can also do something like this

YAHOO.util.Event.addListener(myAnchorDom, "click", this.showScheduler,this,true);

Where myAnchorDom is the achor tag dom object. This will have showScheduler function execute within the scope of your scheduler object.

Answer 3

Instead of working with innerHTML use the DOM methods.

Try replacing this:

header.innerHTML = '<a href="#" onclick="this.showScheduler(1);">Show</a>';

with this:

var x = this; // create a closure reference
var anchor = document.createElement('a');
anchor.href= '#';
anchor.innerHTML = 'Show';
anchor.onclick = function() { x.showScheduler(1); }; //don't use onclick in real life, use some real event binding from a library
header.appendChild(anchor);

Explanation:

The "this" in the original code refers to the element which fired the event, i.e. the anchor ("this' is notoriously problematic for things like, well, like this). The solution is to create a closure on the correct method (which is why you have to create something like the var x above) which then only leaves the problem of passing in the parameter which is accomplished by wrapping the method in another function.

Strictly speaking it would be much preferable to bind eventhandlers with the addEventListener/attachEvent pair (because direct event assignment precludes the ability to assign multiple handlers to one event) but it's best handled using a library like jquery if you're new to JS anyway.

Answer 4

You can add an event handler to the header object directly:

var me = this;

this.setHeader = function(){
          header.innerHTML = '<a href="#" onclick="this.showScheduler(1);">Show</a>';

header.addHandler("click", function(e) { me.showScheduler(1); });
    }

Insite the passed function, this will refer to the header element.

Answer 5

var Scheduler = function(divid, startDate, mode)
{
    var xthis = this;

    this.setHeader = function()
    {
          var lnk = document.createElement("a");
          lnk.addEventListener("click", xthis.showScheduler, false);
          lnk.innerText = "Show";
          lnk.setAttribute('href', "#");
          header.appendChild(lnk);
    }

   this.showScheduler = function period(){

        ...
   }
};

Answer 6

When using "this" inside the onclick attribute, you're actually referring to the anchor tag object. Try this and see if it works:

this.setHeader = function(){
      header.innerHTML = '<a href="#" onclick="Scheduler.showScheduler(1);">Show</a>';
}