- [reduce initial value](#reduce-initial-value)


<section class="qa">
<details>
<summary class="q">

## reduce initial value

QUESTION: What is the problem with both snippets below?

```js
[].reduce((previous, current) => {
  return previous + current;
});

''.split('').reduce((previous, current) => {
  return `${previous}-${current}`;
});
```
</summary>

<div class="a">

ANSWER: Correct:

The problem is that with empty arrays and _no default initial values_ for `reduce`, the JS engine doesn't have anything to return and throws an exception.

TIP: Always provide an initial, default value for your reduces. 0 or 1 for reduces that sum or subtract, 1 for addition and subtraction, empty string for strings. For other cases, consider each one carefully.

```js
[].reduce((previous, current) => {
  return previous + current;
}, 0);

''.split('').reduce((previous, current) => {
  return `${previous}-${current}`;
}, '');
```
</div>
</details>
</section>