Const vs Let in JavaScript.

Javascript Web Development Object Oriented Programming

Const and let were introduced in ES2015 to declare block scoped variables. While variables declared using let can be reassigned, they cannot be reassigned if they were declared using const.

Following is the code showing let and const 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,.sample {
      font-size: 20px;
      font-weight: 500;
   }
</style>
</head>
<body>
<h1>Const and let in JavaScript</h1>
<div class="sample"></div>
<div style="color: green;" class="result"></div>
<button class="Btn">CLICK HERE</button>
<h3>Click on the above button to reassign const and let value</h3>
<script>
   let resEle = document.querySelector(".result");
   let sampleEle = document.querySelector(".sample");
   let a = 22;
   const b = 44;
   sampleEle.innerHTML = "let a = " + a + " ";
   sampleEle.innerHTML += "const b = " + b;
   document.querySelector(".Btn").addEventListener("click", () => {
      a = 99;
      resEle.innerHTML = "Reassigning a = " + a + " ";
      try {
         changeB();
      }
      catch (err) {
         resEle.innerHTML += "Reassigning b = " + err;
      }
   });
   function changeB() {
      b = 22;
   }
</script>
</body>
</html>