JavaScript call() Method

In this chapter, we will learn about the call() method in JavaScript. The call() method is used to call a function with a given this value and arguments provided individually. It allows you to invoke a function with a specific this context, which can be useful in various scenarios. We will cover:

• What is the call() Method?
• Syntax of the call() Method
• Using call() to Invoke Functions
• Borrowing Methods with call()
• Using call() for Method Chaining
• Simple Programs using call()

What is the call() Method?

The call() method is a built-in JavaScript function that allows you to call a function with a specified this value and arguments. It is used for controlling the context in which a function is executed.

Syntax of the call() Method

Syntax

function.call(thisArg, arg1, arg2, ...); 

• thisArg: The value to be used as the this value inside the function.
• arg1, arg2, ...: Arguments to be passed to the function.

Using call() to Invoke Functions

The call() method can be used to invoke functions and explicitly specify the this context.

Example

function greet() { console.log(`Hello, my name is ${this.name}`); } let person = { name: "Ramesh" }; greet.call(person); 

Output:

Hello, my name is Ramesh 

Borrowing Methods with call()

You can use the call() method to borrow methods from one object and use them on another object.

Example

let person1 = { name: "Rahul", age: 25, greet: function() { console.log(`Hello, my name is ${this.name} and I am ${this.age} years old.`); } }; let person2 = { name: "Neha", age: 30 }; person1.greet.call(person2); 

Output:

Hello, my name is Neha and I am 30 years old. 

Using call() for Method Chaining

The call() method can be useful for method chaining, allowing you to call multiple methods in a sequence with a specific this context.

Example

function setDetails(name, age) { this.name = name; this.age = age; } function introduce() { console.log(`My name is ${this.name} and I am ${this.age} years old.`); } let person = {}; setDetails.call(person, "Ramesh", 25); introduce.call(person); 

Output:

My name is Ramesh and I am 25 years old. 

Simple Programs using call()

Program 1: Calculating Area and Perimeter of a Rectangle

function Rectangle(width, height) { this.width = width; this.height = height; } function calculateArea() { return this.width * this.height; } function calculatePerimeter() { return 2 * (this.width + this.height); } let rect = new Rectangle(10, 5); let area = calculateArea.call(rect); let perimeter = calculatePerimeter.call(rect); console.log("Area:", area); console.log("Perimeter:", perimeter); 

Output:

Area: 50 Perimeter: 30 

Program 2: Using call() to Sort an Array of Objects

let people = [ { name: "Ramesh", age: 25 }, { name: "Neha", age: 30 }, { name: "Rahul", age: 20 } ]; function compareAge(a, b) { return a.age - b.age; } people.sort(compareAge.call.bind(compareAge)); console.log(people); 

Output:

[ { name: 'Rahul', age: 20 }, { name: 'Ramesh', age: 25 }, { name: 'Neha', age: 30 } ] 

Conclusion

In this chapter, you learned about the call() method in JavaScript, including its syntax and how to use it to invoke functions with a specific this context, borrow methods, and chain methods. We also provided various use cases with simple programs to demonstrate the usage of the call() method. Understanding how to effectively use the call() method is essential for writing flexible and maintainable JavaScript code.