This and That, and JavaScript

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Recently, I saw this in a classroom and it reminded me of how I use it in JavaScript.

To overcome some of the requirements, we have to create client side scripting in an object oriented way. For an example, client side scripting for a custom server control. Anyways, I’m not going to show how to create a custom server control now. Perhaps, another day.

I created a demo page for this topic. I design a JavaScript class for this page with 3 public functions (Container, Push and Pop) and 1 public property (SequenceId).

function Demo() {
    var that = this;
    this.SequenceId = 1;

    Demo.prototype.Container = function () {
        return $(".Container");
    };

    Demo.prototype.Push = function () {
        this.Container().append("<div class='Item'>" + this.SequenceId + "</>");
        this.SequenceId += 1;
    };

    Demo.prototype.Pop = function () {
        if (this.Container().children().length > 0) {
            this.Container().children().first().remove();
        }
    };

    function AddHandler() {
        $("#Add").click(function (s, e) {
            that.Push();
        });

        $("#Remove").click(function (s, e) {
            that.Pop();
        });
    }

    AddHandler();
}

You can see I created a variable that and assigned it with this object. (In JavaScript, this represent the current instant of the object.) This is because I’m going to re-use the functions of current instant at function body.

Let me explain this JavaScript class.

• function AddHandler(): I use this private method to register all event handler of controls so that I can have no JavaScript in my page. In this function body, I’m going to use Push and Pop functions which were created as public function. I cannot use this.Push or this.Pop because they will actually point to nothing since the this object actually represents the button control.

  

• this.SequenceId: This is a property of this class object. I use it to store the current running number. It will print on every item.
• Demo.prototype.Push: This is a public function so the this object in this function body actually represents the instant of the class.

  

To know more about this, you can refer to Douglas Crockford’s Private Members in JavaScript.