# Loops — JavaScript

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

> for, while, and the two iteration flavors.

## for, while, do...while

`for` fits a known count; `while` fits an unknown one; `do...while` always runs at least once.

```js
for (let i = 0; i < 3; i++) console.log(i);

let n = 3;
while (n > 0) {
  console.log(n);
  n--;
}
```

## for...of vs for...in

`for...of` iterates **values** (arrays, strings); `for...in` iterates **keys** (object properties).

```js
const arr = [10, 20, 30];
for (const val of arr) console.log(val);

const obj = { a: 1, b: 2 };
for (const key in obj) console.log(key, obj[key]);
```

## break & continue

`break` exits the loop entirely; `continue` skips to the next iteration without exiting.

**Quiz:** Which loop is best for iterating an object's own property keys?

- [ ] for...of
- [x] for...in
- [ ] while

*Answer:* for...in. `for...in` is built specifically for enumerating an object's keys.