How to declare variables in JavaScript?

JavaScript variables can be imagined as containers that store data values. Instead of repeating the same value over and over in a script, a variable is declared to represent this value, making coding more efficient and readable.

Steps to Declare a Variable in JavaScript:

1. Use the var Keyword (ES5 and Earlier):

  • Introduced with the first versions of JavaScript and was the standard way to declare variables.


var name = "John";

2. Use the let Keyword (ES6/ES2015 and Later):

  • Part of the ECMAScript 6 standard (also known as ES6 and ES2015).
  • Allows you to declare block-scoped variables.


let age = 25;

3. Use the const Keyword (ES6/ES2015 and Later):

  • For declaring variables whose values shouldn’t change (constants).
  • Block-scoped like let.


const PI = 3.14159;

4. Initialize Without a Keyword (Not Recommended):

  • It’s possible but not advisable due to potential issues and unintended global scope.


mistake = "This is not recommended";


Can I re-declare a variable using let in the same scope?

No. If you’ve already declared a variable using let in a specific scope, re-declaring it in the same scope will result in an error.

What’s the main difference between var and let?

The main difference is scope. Variables declared with var are function-scoped, whereas variables declared with let are block-scoped. This means let variables have a narrower scope, making them preferable in many coding situations for better readability and avoiding potential variable reassignment bugs.

When should I use const?

Use const when you have a variable whose value you don’t want to change or reassign throughout the code. It ensures immutability for the binding, but remember, if you assign an object to a const variable, the object’s properties can still be changed.

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