How to add method to String class in JavaScript ?

In this article, the task is to add a method to the String class in JavaScript. There are two approaches that are described with the proper examples: 

Approaches to add Methods to String Class:

• using Object.defineProperty() method
• using String.prototype.propertyName method

Approach 1: Using Object.defineProperty() method

The Object.defineProperty() method is used to define a new property directly to an object or modify an existing property. It takes 3 arguments, the first is Object, the Second is propertyName, and the last is propertyDescription. In this example, the sum of the length of strings is returned.

Syntax:

Object.defineProperties(obj, props) 

Example: This example uses the above-explained approach.

Javascript

// Input string
let str1 = "GeeksforGeeks";
let str2 = "A Computer Science Portal";

// Display input string
console.log(str1);
console.log(str2);


// Define custom method
Object.defineProperty(String.prototype, "SumOfLength", {
    value: function (param) {
        return this.length + param.length;
    },
});

// Run custom method
function GFG_Fun() {
    // Apply custom method
    let res = str1.SumOfLength(str2);

    // Display output
    console.log("Total length: " + res);
}

// Funcion call
GFG_Fun();

Output

GeeksforGeeks
A Computer Science Portal
Total length: 38

Approach 2: Using String.prototype.propertyName method

The String.prototype.propertyName is used to add a new method to the String class. Define a method that takes arguments passed by the object and performs the desired operation. In this example, the sum of the length of strings is returned.

Syntax:

object.prototype.name = value

Example: This example uses the above-explained approach.

Javascript

// Input string
let str1 = "JavaScript";
let str2 = "A Scripting Language for Web";

// Display input string
console.log(str1);
console.log(str2);

// Define custom method
String.prototype.SumOfLength = function (arg) {
    return this.length + arg.length;
};

// Run custom method
function GFG_Fun() {
    // Apply custom method
    let res = str1.SumOfLength(str2);

    // Display output
    console.log("Total length: " + res);
}

// Funcion call
GFG_Fun();

Output

JavaScript
A Scripting Language for Web
Total length: 38