DEV Community

Michael Fazekas
Michael Fazekas

Posted on

2 1

let vs var keyword

If you're new to learning JavaScript and have taken courses on youtube or anything other platform and don't really understand the difference between let and var or wondering why var isn't a standard in JavaScript anymore.
SAY NO MORE!

Image description

Let

first let's start with let. Let was introduced in ECMASCRIPT 6 === ES6 but you could use it a little bit in es5 for limited scope declarations. Wasn't until es6 that let and const were formerly introduced.

Stop using VAR!

Let is a great way to prevent bugs in your code. why you ask?

Image description

Because let is only limited to the scope of the block of code.
so lets say you have a function.

function user(){
let name = 'mike'
}

but you have another let name outside of the function.


let name = 'james';

remember all functions can access the global or root scope. so with let you cant reassign it, it can be modified but only inside the block scope.

Like this:

let = wizardLevel = false
function user(){
     wizardLevel = true;
    console.log('function',wizardLevel) <== returns true
}

user();
console.log(wizardLevel) <=== returns false
// because it happened outside of the function scope.

Enter fullscreen mode Exit fullscreen mode

Look How var is accessed in if statment

var wizardLevel = false;
var experience = 100;
if(experience > 90){
     wizardLevel = true;
    console.log('inside',wizardLevel);
}

console.log('outside', wizardLevel);
Enter fullscreen mode Exit fullscreen mode

Both wizardLevel variables will return true because of access to the scope. see image for results

Image description

Do your career a big favor. Join DEV. (The website you're on right now)

It takes one minute, it's free, and is worth it for your career.

Get started

Community matters

Top comments (0)

Image of Docusign

🛠️ Bring your solution into Docusign. Reach over 1.6M customers.

Docusign is now extensible. Overcome challenges with disconnected products and inaccessible data by bringing your solutions into Docusign and publishing to 1.6M customers in the App Center.

Learn more