ES6 - Difference Between Var And Let

To declare the variables in JavaScript or TypeScript, we often use var or let. Here, we will discuss the differences between both of the declarations.

Overview

 

To declare the variables in JavaScript or TypeScript, we often use var or let. Here, we will discuss the differences between both of the declarations. 

 

var

 

When we declare variables using var:

1. The declaration is processed before the execution.
2. Variable will have function scope.

Code

function CheckingScope() {
    var _scope = ‘Out’;
    console.log(_scope); // output Out
    if (true) {
        var _scope = ‘In’;
        console.log(_scope); // output In
    }
    console.log(_scope); // output In
}

In the above code, we can find that when the variable is updated inside the if block, the value of variable "_scope" is updated to “In” globally.

 

let

 

When we declare variables using let:

1. Variable will have block scope. 

Code

function CheckingScope() {
    var _scope = ‘Out’;
    console.log(_scope); // output Out
    if (true) {
        let _scope = ‘In’;
        console.log(_scope); // output In
    }
    console.log(_scope); // output Out
}

In the above code, we can find that when the variable is updated inside the if block, the value of variable "_scope" is not updated globally.

 

Reference

• https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Statements/let