Example #
var person = {
firstName: "John",
lastName : "Doe",
id : 5566,
fullName : function() {
return this.firstName + " " + this.lastName;
}
};
What is this? #
The JavaScript this
keyword refers to the object it belongs to.
It has different values depending on where it is used:
- In a method,
this
refers to the owner object. - Alone,
this
refers to the global object. - In a function,
this
refers to the global object. - In a function, in strict mode,
this
isundefined
. - In an event,
this
refers to the element that received the event. - Methods like
call()
, andapply()
can referthis
to any object.
this in a Method #
In an object method, this
refers to the “owner” of the method.
In the example on the top of this page, this
refers to the person object.
The person object is the owner of the fullName method.
fullName : function() {
return this.firstName + " " + this.lastName;
}
var x = this;
In strict mode, when used alone, this
also refers to the Global object [object Window]
:
Example #
"use strict";
var x = this;
function myFunction() {
return this;
}
"use strict";
function myFunction() {
return this;
}
<button onclick="this.style.display='none'">
Click to Remove Me!
</button>
var person = {
firstName : "John",
lastName : "Doe",
id : 5566,
myFunction : function() {
return this;
}
};
Example #
var person = {
firstName: "John",
lastName : "Doe",
id : 5566,
fullName : function() {
return this.firstName + " " + this.lastName;
}
};
In other words: this.firstName means the firstName property of this (person) object.
Explicit Function Binding #
The call()
and apply()
methods are predefined JavaScript methods.
They can both be used to call an object method with another object as argument.
You can read more about call()
and apply()
later in this tutorial.
In the example below, when calling person1.fullName with person2 as argument, this
will refer to person2, even if it is a method of person1:
Example #
var person1 = {
fullName: function() {
return this.firstName + " " + this.lastName;
}
}
var person2 = {
firstName:"John",
lastName: "Doe",
}
person1.fullName.call(person2); // Will return "John Doe"