Why const over let

Why const over let

Is it true that const makes a variable immutable?

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In this article, I want to discuss why I prefer const over let when declaring variables in JavaScript.

Truth about const

Variables declared with const often come across as being immutable. Now, if you have written JavaScript for a while, you know that they aren't immutable, rather, they can't be reassigned.

const arr = [];

// This is valid, because we aren't reassigning the variable, 
// but mutating it instead.

// This is NOT valid, because we are reassigning the 
// variable which was declared using const
arr = [22222]

Why const?

If both const and let variables can be mutated/changed, does it really matter which one we pick?

In my opinion, yes it does.

We should stick to const whenever we can, and whenever we need to reassign variables, then we should use let.

Problem with reassignment

Reassignments are wrong, they are a code smell, and they aren't good to write, avoid them whenever you can.

The reason for reassignments being bad goes back to the single responsibility principle.

If a variable is responsible for multiple values, the code gets harder to maintain and the chance for bugs to get introduced is higher.

The mental effort to understand the code when variables have multiple responsibilities is higher, meaning, introducing a higher burden.

This also goes back to the statement that code should be written to be easy to read, not for writing convenience.


This is my take, and some thoughts I've had for a while after seeing people saying it doesn't really matter whether you go with let or const, and some don't even care at all, even if you mix them and things look not so nice, to use nice language here.