What are function expressions in JavaScript?

Javascript Web Development Object Oriented Programming

Function expressions allow us to store the function in a variable that can be later invoked using the variable name. They also aren’t hoisted like normal function declaration so they can’t be called before they are defined.

Following is the code to implement function expressions in JavaScript −

Example

Live Demo

<!DOCTYPE html>
<html lang="en">
<head>
<meta charset="UTF-8" />
<meta name="viewport" content="width=device-width, initial-scale=1.0" />
<title>Document</title>
<style>
   body {
      font-family: "Segoe UI", Tahoma, Geneva, Verdana, sans-serif;
   }
   .result {
      font-size: 18px;
      font-weight: 500;
      color: rebeccapurple;
   }
</style>
</head>
<body>
<h1>Function expression in JavaScript</h1>
<div class="result"></div>
<button class="Btn">CLICK HERE</button>
<h3>Click on the above button to display a function expression</h3>
<script>
   let resultEle = document.querySelector(".result");
   let a = function () {
      return "This is a function expression";
   };
   document.querySelector(".Btn").addEventListener("click", () => {
      resultEle.innerHTML = " a = " + a + "<br>";
      resultEle.innerHTML += " a() = " + a() + "<br>";
   });
</script>
</body>
</html>