---
name: "up.util.filter"
area: "API"
kind: "JavaScript function"
parent: "up.util module"
url: "https://unpoly.com/api/up.util.filter"
---
<nav aria-label="Unpoly docs">[All docs](https://unpoly.com/index.md) · [up.util module](https://unpoly.com/api/up.util.md)</nav>

# up.util.filter(list, tester)

Returns all elements from the given [list](https://unpoly.com/api/List.md) that return a truthy value when passed to the given function.

---

## Parameters {#parameters}

### list {#list}

(required)

Type: [List](https://unpoly.com/api/List.md) | Iterator

### tester {#tester}

(required)

Type: Function(value, index): boolean

---

## Return value {#return-value}

Type: [Array](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Array)