# Let vs Const in JavaScript

> Should you use let or const in JavaScript? My take: default to const because it prevents reassignment, and only reach for let when you truly need to reassign.

Author: [Flavio Copes](https://flaviocopes.com/about/) | Published: 2020-03-25 | Topics: [JavaScript](https://flaviocopes.com/tags/js/) | Canonical: https://flaviocopes.com/javascript-let-const/

In [JavaScript](https://flaviocopes.com/javascript/), we commonly declare variables using two keywords: `let` and `const`.

When should we use one vs the other?

I always default to using `const`. 

Why? 

Because `const` guarantees the value can’t be reassigned.

When programming, I always think that the best thing that I can use is the thing that can harm me the least.

We have an incredible amount of things that can generate problems.

The more power you give to something, the more responsibility you assign to it.

And we don't generally want that.

Well, it's debatable, of course, as everything. *I* don't want that, and that's enough for me.

If I declare a variable using `let`, I *let* it be reassignable:

```js
let number = 0
number = 1
```

and in some cases this is necessary.

If I **want** the variable to be reassignable, `let` is perfect.

If I don't, which is in 80% of the cases, I don't even what that option be available. I want the compiler (interpreter, in the case of JS) to give me an error.

That's why I default to `const` every time I declare a variable, and only switch to `let` when I want the reassign ability to be allowed.