Variable Declaration

A variable declaration is when you create a variable to store a value in JavaScript. You give it a descriptive name, which you can then use to store or retrieve the value. In JavaScript, you use var, let, and const keywords to declare variables.

Older versions of JavaScript used the var keyword to declare variables**.** Variables declared using the var keyword have a function scope. It lets you give variables the same name and a new value even in the same scope. However, it may result in confusion and errors, making debugging your code difficult.

var course = "java";

var course = "JavaScript interview questions"; // No error

console.log(course); // JavaScript interview questions

The let keyword is a new way to declare variables in JavaScript in ECMAScript 2015 (ES6). Variables declared using the let keyword have a block scope. You can change the value, but you can't use the same name for a variable in the same block scope. It helps make debugging code easier compared to the var keyword.

let course = "java";

let course = "JavaScript interview questions"; 

console.log(course);// Identifier 'course' has already been declared



// Example 2

let course = "java";

course = "JavaScript interview questions"; 

console.log(course);// JavaScript interview questions

The const keyword works as the let keyword since both are block-scoped. However, you cannot change the value or use the same name for a variable in the same scope.

const course = "java";

course = "JavaScript interview questions"; 

// Error: Assignment to constant variable.