Example
var person = {
firstName: “John”,
lastName : “Doe”,
id : 5566,
fullName : function() {
return this.firstName + ” ” + this.lastName;
}
};
What is “this”?
In a function definition, this refers to the “owner” of the function.
In the example above, this refers to the person object.
The person object “owns” the fullName method.
Default Binding
When used alone, this refers to the Global object.
In a browser the Global object is [object Window]:
When used in a function, this refers to the Global object.
Example
function myFunction() {
return this;
}
In strict mode, this will be undefined, because strict mode does not allow default binding:
Example
“use strict”;
function myFunction() {
return this;
}
Object Method Binding
In these examples, this is the person object (The person object is the “owner” of the function):
Example
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 an other object as argument.
You can read more about call() and apply() later in this tutorial.
In this example, 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”