JavaScript: var, let and const

In this article, I have explained the difference between var, let and const in ES6.

In ES5, we were able to declare variables using var only. But in ES6, we have three ways to declare variables in JavaScript: var, let and const. Here, we will explore the what, why, and how of var, let and const with examples.

var

• Scope of var is global or function level. Variable declared within a function has the function level scope otherwise global scope.
• Can be re-declared multiple times using var key word and same variable name.
• Value of variable declared using var can be updated anywhere within the scope.

Sample Code:

let

• Scope of let is block level. Here block is confined to the curly braces ({ and } like function, if or for blocks etc.).
• Variables declared within curly braces can not be accessed from outside the respective scopes.
• Can not be re-declared multiple times using let keyword and same variable name.
• Value of variables declared using let can also be updated anywhere within the scope.

Sample code:

const

• Scope of const is same as let, block level. Here block is confined to the curly braces ({ and }).
• Variables declared within curly braces can not be accessed from outside the respective scopes.
• Can not be re-declared multiple times using const keyword and same variable name.
• Value can not be updated once value is assigned to a const. But properties can be updated.

Sample code:

Please share your thoughts in comments.

Thanks!