Calling a Class function from within a class in Javascript, Jquery

You need to pass anonymously function for that:

this.xId = window.setInterval( function() { this.run() }, 2500 );

Or better is to bind this function with this context:

this.xId = window.setInterval( this.run.bind(this) , 2500 );

Note that bind are implemented in ECMA-262, 5th edition, so for crossbrowser compatibility you need to add this:

if (!Function.prototype.bind) {  
  Function.prototype.bind = function (oThis) {  
    if (typeof this !== "function") {  
      // closest thing possible to the ECMAScript 5 internal IsCallable function  
      throw new TypeError("Function.prototype.bind - what is trying to be bound is not callable");  
    }  

    var aArgs = Array.prototype.slice.call(arguments, 1),   
        fToBind = this,   
        fNOP = function () {},  
        fBound = function () {  
          return fToBind.apply(this instanceof fNOP  
                                 ? this  
                                 : oThis || window,  
                               aArgs.concat(Array.prototype.slice.call(arguments)));  
        };  

    fNOP.prototype = this.prototype;  
    fBound.prototype = new fNOP();  

    return fBound;  
  };  
}

• First of all, use a function reference rather than a string for the timeout callback. the this when using a string is the global object, and not what might have provided it.

• Secondly, cache the value of this. The this in the callback may not be the same as the one outside it (which is the one attached with run).

  function(){
      var that = this; //cache "this"
  
      this.run = function(){
          //DO SOMETHING;
      }
  
      this.xId = window.setInterval(function(){
          that.run()
      },2500);
  }