JavaScript Function call()
Method Reuse
With the call() method, you can write a method that can be used on different
objects.
All Functions are Methods
In JavaScript all functions are object methods.
If a function is not a method of a JavaScript object, it is a function of the global object (see previous chapter).
The example below creates an object with 3 properties, firstName, lastName, fullName.
Example
firstName:"John",
lastName: "Doe",
fullName: function () {
return this.firstName + " " + this.lastName;
}
}
// This will return "John Doe":
person.fullName();
In the example above, this refers to the person object.
this.firstName means the firstName property of this.
Same as:
this.firstName means the firstName property of person.
What is this?
In JavaScript, the this keyword refers to an object.
The this keyword refers to different objects depending on how it is used:
this refers to the global object.this refers to the global object.this is undefined.this refers to the object.this refers to the element that received the event.call(), apply(),
and bind() can refer this to any object.Note
this is not a variable.
this is a keyword.
You cannot change the value of this.
The JavaScript call() Method
The call() method is a predefined
JavaScript method.
It can be used to invoke (call) a method with an object as an argument (parameter).
Note
With call(), an object can use a method belonging to another object.
This example calls the fullName method of person, using it on person1:
Example
fullName: function() {
return this.firstName + " " + this.lastName;
}
}
const person1 = {
firstName:"John",
lastName: "Doe"
}
const person2 = {
firstName:"Mary",
lastName: "Doe"
}
// This will return "John Doe":
person.fullName.call(person1);
This example calls the fullName method of person, using it on person2:
Example
fullName: function() {
return this.firstName + " " + this.lastName;
}
}
const person1 = {
firstName:"John",
lastName: "Doe"
}
const person2 = {
firstName:"Mary",
lastName: "Doe"
}
// This will return "Mary Doe"
person.fullName.call(person2);
The call() Method with Arguments
The call() method can accept arguments:
Example
fullName: function(city, country) {
return this.firstName + " " + this.lastName + "," + city + "," + country;
}
}
const person1 = {
firstName:"John",
lastName: "Doe"
}
person.fullName.call(person1, "Oslo", "Norway");