4.3 This

>>>

this

[object Window]

The this keyword provides access to the current object context. In the outermost scope, it points to the window object in web browsers.

>>>

function MyObject(val) {
    this.a = val;
    this.b = 'test';
}

Inside constructor functions, this references the new object instance created.

>>>

var obj = new MyObject(123);

>>>

obj

{ "a": 123, "b": "test" }

Using this, the constructor function can initialize and modify the new instance.

>>>

function example() {
    return 'a = ' + this.a + ', b = ' + this.b;
}

>>>

example()

"a = undefined, b = undefined"

Inside normal functions, using this is mostly pointless (or even erroneous).

>>>

obj.toString = example;

But if the function is bound to an object property, it can be called as a method of the object.

>>>

obj.toString()

"a = 123, b = test"

When functions are called as object methods, this is automatically bound to the object in question. This binding happens at call-time.

>>>

'str: ' + obj

"str: a = 123, b = test"

Also note that toString() is the special method used when coercing an object to a string.

>>>

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