JavaScript Function Definitions

The function definition basically consists of the keyword function and then the name of the function, the function parameters and a set of curly braces enclosing the JavaScript statements.

Following is the code for implementing function definitions in JavaScript −


 Live Demo

<!DOCTYPE html>
<html lang="en">
<meta charset="UTF-8" />
<meta name="viewport" content="width=device-width, initial-scale=1.0" />
   body {
      font-family: "Segoe UI", Tahoma, Geneva, Verdana, sans-serif;
   .sample {
      font-size: 18px;
      font-weight: 500;
<h1>JavaScript Function Definitions</h1>
<div class="sample"></div>
<button class="Btn">CLICK HERE</button>
<h3>Click on the above buttons to see the function definitions</h3>
   let sampleEle = document.querySelector(".sample");
   function helloWorld() {
      alert("HELLO WORLD");
   let testFunction = function () {
      alert("TEST FUNCTION");
   document.querySelector(".Btn").addEventListener("click", () => {
      sampleEle.innerHTML = helloWorld + "<br>" + testFunction;


On clicking the “CLICK HERE” button −