NodeJS
Understanding Call, Apply, and Bind in JavaScript
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Introduction
Here, first we will discuss why we need to require the call,apply & bind methods are required.So, first we will start with the problem statement with an example.
Problem Statement Example
The example below creates an object with 3 properties, firstName, lastName, fullName.
const person = { firstName:"John", lastName: "Doe", fullName: function () { return this.firstName + " " + this.lastName; }}// This will return "John Doe":person.fullName();const person2 = { firstName:"Kelvin", lastName: "Saw", fullName: function () { return this.firstName + " " + this.lastName; }}// This will return "Kelvin Saw":person2.fullName();
You can see that the same function is being called multiple times, which causes duplication and is not reusable. There are three methods provided in JavaScript to solve this problem: Call,Apply & Bind.
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).
Example:
function showName() { return this.firstName + " " + this.lastName;}const person = { firstName: "John", lastName: "Doe"};console.log(showName.call(person)); // Output: "John Doe"const person2 = { firstName: "Kelvin", lastName: "Saw"};console.log(showName.call(person2)); // Output: "Kelvin Saw"
The call() Method with Arguments
function showName(city,country) { return this.firstName + " " + this.lastName + "," + city + "," + country; ;}const person = { firstName: "John", lastName: "Doe"};console.log(showName.call(person,"Ahmedabad","India")); // Output: "John Doe, Ahmedabad, India"const person2 = { firstName: "Kelvin", lastName: "Saw"};console.log(showName.call(person2,"Maxico","US")); // Output: "Kelvin Saw, Maxico, US"
Apply Method
The apply method works similarly to call, but it takes an array of arguments instead of listing them individually.
Example:
function showName(city,country) { return this.firstName + " " + this.lastName + "," + city + "," + country; ;}const person = { firstName: "John", lastName: "Doe"};console.log(showName.apply(person,["Ahmedabad","India"])); // Output: "John Doe, Ahmedabad, India"const person2 = { firstName: "Kelvin", lastName: "Saw"};console.log(showName.apply(person2,["Maxico","US"])); // Output: "Kelvin Saw, Maxico, US" Bind Method
The bind method returns a new function with a permanently bound this value. Unlike call and apply, bind does not execute the function immediately.
Example:
function greeting(greetingMsg) { return greetingMsg + "," + this.firstName + " " + this.lastName;}const person = { firstName: "John", lastName: "Doe"};const bindMethod = greeting.bind(person,"Hello");//When you need to retrieve the data, call the method like this:console.log(bindMethod());// Output: Hello, John Doe Ready to transform your business with our technology solutions? Contact Us today to Leverage Our NodeJS Expertise.
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