# Variables: let, const, var — JavaScript

Source: https://www.geekswithgeeks.com/en/javascript/js-variables

> Three ways to declare, and why const should be your default.

## Declaring variables

`let` can be reassigned, `const` cannot, and `var` is the old, function-scoped way.

```js
let age = 25;
age = 26;          // OK

const name = "Ada";
// name = "Bo";    // TypeError

var legacy = "old style";
```

## Block vs function scope

`let`/`const` are **block-scoped** — confined to `{ }`. `var` is **function-scoped** and leaks out of blocks like `if` or `for`.

## Default to const

Use `const` unless you know the value will change, then reach for `let`. Avoid `var` in modern code.

## const with objects

`const` locks the *binding*, not the contents — an object or array declared with `const` can still be mutated.

```js
const user = { name: "Ada" };
user.name = "Grace";   // allowed
console.log(user);
```

Output:

```
{ name: 'Grace' }
```