JavaScript: Add Method to Prototype

By Xah Lee. Date: . Last updated: .

This page shows you how to add method to prototype objects.

Add Method to String Prototype

Example of adding a method to String.prototype

// add a removeVowels method for string prototype

String.prototype.removeVowels = function () {
  return this.replace(/[aeiou]/g, "");

// example call
console.log("how are you".removeVowels() === "hw r y");

Add Method to Array Prototype

Example of adding a method to Array.prototype

// add a method to array prototype

// remove first and last item of a array, return the removed items as array

Array.prototype.shiftAndPop = function () {
  return [this.shift(), this.pop()];

// ssss---------------------------------------------------
// test
const xx = [0, 1, 2, 3, 4];

  JSON.stringify(xx.shiftAndPop()) === "[0,4]",

  JSON.stringify(xx) === "[1,2,3]",

Add Method to Number Prototype

Example of adding a method to Number.prototype

// add a method to the number prototype
Number.prototype.plusN = function (n) {
  return (this + n);

// test
console.log(3["plusN"](4) === 7);

πŸ’‘ TIP: Do Not Add to Object Prototype

Adding a method to prototype is not a recommended practice. Because, adding to global object changes the language unexpectedly and create conflicts if other people also do it.

[see Prototype and Inheritance]

JavaScript Object and Inheritance

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