# Get indices of a value in an array

Collect every index where a value appears.

Canonical: https://1loc.dev/array/get-indices-of-a-value-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 indices({ values, value }) { return values.flatMap((item, i) => (item === value ? [i] : [])); }
```

## Input

```json
{
  "values": [
    "a",
    "b",
    "a",
    "c"
  ],
  "value": "a"
}
```

## Expected output

```json
[
  0,
  2
]
```

## Edge case

Input:
```json
{
  "values": [
    1,
    2
  ],
  "value": 3
}
```
Output:
```json
[]
```

## Limits

- The original second variant dropped index 0, because filter(Boolean) removes it; flatMap keeps it.

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/get-indices-of-a-value-in-an-array.mdx
Author: Nguyen Huu Phuoc and original contributors
Contributors: See original repository history
Source commit: 14b481cf60dff1620ab1bb99a43b1f68068cdd9b
Copyright (c) 2020 phuoc-ng
License: MIT — https://1loc.dev/licenses/
Maintainer: Oveyon
Modifications: Uses flatMap; the original second variant dropped index 0 with filter(Boolean). Original MDX retained as inert source evidence.