To add all numbers in an array in JavaScript, do this:

`array.reduce((a, b) => a + b, 0)`

.Here's how you do it:

```
const array = [ 1, 2, 3 ];
const sum = array.reduce((a, b) => a + b, 0);
console.log(sum); // 6
```

+

To add all numbers in an array in JavaScript, do this:

`array.reduce((a, b) => a + b, 0)`

.Here's how you do it:

```
const array = [ 1, 2, 3 ];
const sum = array.reduce((a, b) => a + b, 0);
console.log(sum); // 6
```