// Tutorial //

Let and Const in JavaScript with ES6 / ES2015

Published on November 10, 2016
Default avatar

By Alligator.io

Let and Const in JavaScript with ES6 / ES2015

While we believe that this content benefits our community, we have not yet thoroughly reviewed it. If you have any suggestions for improvements, please let us know by clicking the “report an issue“ button at the bottom of the tutorial.

Two new keywords are available in ES6 / ES2015 to declare variables in JavaScript: let and const. Contrary to var, let and const are block-scoped.

Var has an issue where it’s not block-scoped, which can lead to surprises:

var dog = 'Ralf';

if (true) {
  var dog = 'Skip';
}

console.log(dog); // Skip

Compare this to using let:

let dog = 'Ralf';

if (true) {
  let dog = 'Skip';
}

console.log(dog); // Ralf

Var is properly function-scoped, meaning that the issue doesn’t happen in functions, but in blocks like if or for all bets are off and variables declared with var get hoisted to the parent scope.

Const

With const you can define immutable variables (constants). Trying to re-assign a constant will raise an error:

const PI = 3.1415;

PI = 5; // "TypeError: Assignment to constant variable.

Be careful however, new items can still be pushed into an array constant or added to an object. The following 2 snippets work without complaining because we are not trying to reassign to the variables:

const someArr = [3, 4, 5];

someArr.push(6);
const someObj = {
  dog: 'Skip',
  cat: 'Caramel',
  bird: 'Jack'
};

someObj.camel = 'Bob';

Let vs Var

Many developers now agree that there’s not a very strong case for using var at all anymore and that using let should be the way to go forward.

In short, use let!

Thanks for learning with the DigitalOcean Community. Check out our offerings for compute, storage, networking, and managed databases.

Learn more about us


Want to learn more? Join the DigitalOcean Community!

Join our DigitalOcean community of over a million developers for free! Get help and share knowledge in our Questions & Answers section, find tutorials and tools that will help you grow as a developer and scale your project or business, and subscribe to topics of interest.

Sign up now
About the authors
Default avatar
Alligator.io

author

Still looking for an answer?

Ask a questionSearch for more help

Was this helpful?
 
Leave a comment
Leave a comment...

This textbox defaults to using Markdown to format your answer.

You can type !ref in this text area to quickly search our full set of tutorials, documentation & marketplace offerings and insert the link!

Try DigitalOcean for free

Click here to sign up and get $200 of credit to try our products over 60 days!
Try DigitalOcean for free