Declaring a variable in JS

Well, there is a thing that always confused me; which method should we use to declare a variable 😵?

Well, if you are like me, then get ready to dive deep!

var

var was introduced in the earliest version of Javascript, and you will find it in legacy codebases (also in Stack Overflow answers 😜).

You might be thinking, "Then what is the problem with it?"

The first problem is re-declaration

In var you can not only reassign the variable but also re-declare it.

Here's an example:

var time = "4pm";
time = "5pm"; // re-assignment
var time = "8pm"; // re-declaration

You may be thinking "Hey! What's the problem with that?" Let me tell you a straightforward answer :- Re-declaring does nothing but induces 🐛. Creepy ones😱.

The second problem is its Scope

var has a global scope(except when it's in a function), which means it can be used anywhere in the code. See this code:

var day = "Wednesday";
if (40 > 3) {
   var day = "Monday";
}

In this code, you will think that you made a new variable day, but didn't notice it was assigned before. This can cause many bugs so in ES6, let and const were introduced.

let

You can think of let as the ES6 version of var. You can do similar things, but it fixes the problems.

The first problem fixed is that you cannot re-declare a variable.

For a demo, see this:

let time = "4pm";
// re-assignment works
time = "5pm";
// re-declaration throws an error
let time = "8pm"; //does not work

The second problem fixed is that let, when defined in a code block, has a scope of only that block.

const

const should be your way of assigning variables all the time when you know the value should not change. It is similar to let, but its value is constant.

Conclusion

Always use const as default, and when you know the value would be changed in the future, use let. Never use var as it will induce bugs in your code.

A quick note

This is my first blog, so if it has any errors, please tell me 😊. THANKS FOR READING !!!