TM. TM. - 1 year ago 66
Javascript Question

What's the difference between using "let" and "var" to declare a variable?

ECMAScript 6 introduced the

statement. I've heard it described as a "local" variable, but I'm still not quite sure how it behaves differently than the

What are the differences? When should
be used over

Answer Source

The difference is scoping. var is scoped to the nearest function block and let is scoped to the nearest enclosing block, which can be smaller than a function block. Both are global if not in a block.

Also, variables declared with let are not accessible before they are declared in their enclosing block. As seen in the demo, this will throw a ReferenceError exception.

Demo: jsFiddle


They are identical when used like this outside a function block.

let me = 'go'; //globally scoped
var i = 'able'; //globally scoped


They are identical when used like this in a function block.

function ingWithinEstablishedParameters() {
    let terOfRecommendation = 'awesome worker!'; //function block scoped
    var sityCheerleading = 'go!'; //function block scoped


Here is the difference. let is only visible in the for() loop and var is visible to the whole function.

function allyIlliterate() {
    //tuce is *not* visible out here

    for( let tuce = 0; tuce < 5; tuce++ ) {
        //tuce is only visible in here (and in the for() parentheses)

    //tuce is *not* visible out here

function byE40() {
    //nish *is* visible out here

    for( var nish = 0; nish < 5; nish++ ) {
        //nish is visible to the whole function

    //nish *is* visible out here

Additionally (Deprecated):

let can also be used to create its own enclosing block.

function conjunctionJunctionWhatsYour() {
    //sNotGetCrazy is *not* visible out here

    let( sNotGetCrazy = 'now' ) {
        //sNotGetCrazy is only visible in here

    //sNotGetCrazy is *not* visible out here
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