JavaScript Function call()

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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

const person = {
  firstName:"John",
  lastName: "Doe",
  fullName: function () {
    return this.firstName + " " + this.lastName;
  }
}

// This will return "John Doe":
person.fullName();  

Try it Yourself »

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.
Which object depends on how this is being invoked (used or called).
The this keyword refers to different objects depending on how it is used:

In an object method, this refers to the object.
Alone, this refers to the global object.
In a function, this refers to the global object.
In a function, in strict mode, this is undefined.
In an event, this refers to the element that received the event.
Methods like call(), apply(),
and bind() can refer this to any object.


Note
this is not a variable. It is a keyword. You cannot change the value of this.


See Also:
The JavaScript this Tutorial








The JavaScript call() Method
The call() method is a predefined
JavaScript method.
It can be used to invoke (call) a method
with an owner object as an argument (parameter).

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

const person = {
  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);


Try it Yourself »


This example calls the fullName method of person, using it on
person2:

Example

const person = {
  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);


Try it Yourself »


The call() Method with Arguments
The call() method can accept arguments:

Example

const person = {
  fullName: function(city, country) {
    return this.firstName + " " + this.lastName
+ "," + city + "," + country;
  }}

const person1 = {
  firstName:"John",
  lastName: "Doe"
}

person.fullName.call(person1, "Oslo", "Norway");


Try it Yourself »














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Reference: https://www.w3schools.com/js/js_function_call.asp