---
title: "js combine iterations"
description: "Multiple `.filter()` or `.map()` calls iterate the array multiple times. Combine into one loop."
type: skill
canonical_url: https://claudary.paisolsolutions.com/skills/js-combine-iterations
source: "Claudary"
difficulty: intermediate
author: "Claude Code Knowledge Pack"
date: 2026-07-10T11:30:22.788Z
license: CC-BY-4.0
attribution: "js combine iterations — Claudary (https://claudary.paisolsolutions.com/skills/js-combine-iterations)"
---

# js combine iterations
Multiple `.filter()` or `.map()` calls iterate the array multiple times. Combine into one loop.

## Overview

---
title: Combine Multiple Array Iterations
impact: LOW-MEDIUM
impactDescription: reduces iterations
tags: javascript, arrays, loops, performance
---

## Combine Multiple Array Iterations

Multiple `.filter()` or `.map()` calls iterate the array multiple times. Combine into one loop.

**Incorrect (3 iterations):**

```typescript
const admins = users.filter(u => u.isAdmin)
const testers = users.filter(u => u.isTester)
const inactive = users.filter(u => !u.isActive)
```

**Correct (1 iteration):**

```typescript
const admins: User[] = []
const testers: User[] = []
const inactive: User[] = []

for (const user of users) {
  if (user.isAdmin) admins.push(user)
  if (user.isTester) testers.push(user)
  if (!user.isActive) inactive.push(user)
}
```

---

Source: [Claudary](https://claudary.paisolsolutions.com/skills/js-combine-iterations) · https://claudary.paisolsolutions.com