# Find the length of the longest string in an array

Map strings to lengths and take the maximum.

Canonical: https://1loc.dev/array/find-the-length-of-the-longest-string-in-an-array/
Version: 1.0.0
Runtime: JavaScript · Node.js 22 / modern browsers
Verification: Local fixtures; no external services
Updated: 2026-10-28

## Implementation

```javascript
function longestLength(words) { return Math.max(0, ...words.map(word => word.length)); }
```

## Input

```json
[
  "ana@example.com",
  "rui@example.com",
  "a@example.co"
]
```

## Expected output

```json
15
```

## Edge case

Input:
```json
[]
```
Output:
```json
0
```

## Limits

- Starting from 0 makes an empty array return 0; the original returned -Infinity.
- Lengths are UTF-16 code units.

The lab validates types and size before calling this function. Add equivalent validation at your own trust boundary.

## Source and license

Original: https://github.com/phuocng/1loc/blob/14b481cf60dff1620ab1bb99a43b1f68068cdd9b/contents/find-the-length-of-the-longest-string-in-an-array.mdx
Author: Nguyen Huu Phuoc and original contributors
Contributors: codepo8
Source commit: 14b481cf60dff1620ab1bb99a43b1f68068cdd9b
Copyright (c) 2020 phuoc-ng
License: MIT — https://1loc.dev/licenses/
Maintainer: Oveyon
Modifications: Returns 0 for an empty array instead of -Infinity. Original MDX retained as inert source evidence.