Let-Const-Var-Differences-In-Js

Let/Const/Var Differences And Use In JavaScript

Source

Var

Var is the original way of declaring variables. Since ES6 came out everything's changed but you can still use var.

Var is globally scoped when outside of a function, but functionally scoped inside of a function.

var greeter = "hey hi"; // Global Scoped

function newFunction() {
    var hello = "hello"; // Function scoped
}

You can also redeclare var and also overwrite it. This can become a problem if we were to use greeter in other parts of our code without intention.

Let

Let is the new and preferred way to declare variables.

Let is block scoped, in that the scope exists within curly braces, {}.

let greeting = "say Hi";
let times = 4;

if (times > 3) {
    let hello = "say Hello instead";
    console.log(hello);// "say Hello instead"
}
console.log(hello) // hello is not defined

Let can also not be redeclared, but it can be overwritten. This helps as we have a mutable variable but we won't run into issues redeclaring later in our code, as it will just error out.

Const

Const is similar to let, but the values will remain constant.

Const is also block scoped.

Const also cannot be redeclared, but it also cannot be overwritten. However, if we create an object using a const we can update it's properties.

const greeting = {
    message: "say Hi",
    times: 4
}

// Can be updated using
greeting.message = "say Hello instead";

#JavaScript