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this keyword

sayHi.alternate = function() {

alert(“hola”);

};

sayHi(); //outputs “hi”

sayHi.alternate(); //outputs “hola”

Here, the method

alternate()

is actually a method on the function

sayHi

. It is possible to call the

sayHi()

as a regular function to output

“hi”

as well as calling

sayHi.alternate()

to output

“hola”

Even so,

alternate()

is considered to be a method of the function

sayHi()

in the public scope, not a

static method.

The this keyword

One of the most important concepts to grasp in ECMAScript is the use of the

this

keyword, which is

used in object methods. The

this

keyword always points to the object that is calling a particular

method, for example:

var oCar = new Object;

oCar.color = “red”;

oCar.showColor = function () {

alert(this.color); //outputs “red”

};

Here, the

this

keyword is used in the

showColor()

method of an object. In this context,

this

is equal

car

, making this code functionality equivalent to the following:

var oCar = new Object;

oCar.color = “red”;

oCar.showColor = function () {

alert(oCar.color); //outputs “red”

};

So why use

this

? Because you can never be sure of the variable name a developer will use when instan-

tiating an object. By using

this

, it is possible to reuse the same function in any number of different

places. Consider the following example:

function showColor() {

alert(this.color);

}

var oCar1 = new Object;

oCar1.color = “red”;

oCar1.showColor = showColor;

var oCar2 = new Object;

oCar2.color = “blue”;

oCar2.showColor = showColor;

oCar1.showColor(); //outputs “red”

oCar2.showColor(); //outputs “blue”

Object Basics

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