1---
2title: Combine Multiple Array Iterations
3impact: LOW-MEDIUM
4impactDescription: reduces iterations
5tags: javascript, arrays, loops, performance
6---
7 
8## Combine Multiple Array Iterations
9 
10Multiple `.filter()` or `.map()` calls iterate the array multiple times. Combine into one loop.
11 
12**Incorrect (3 iterations):**
13 
14```typescript
15const admins = users.filter(u => u.isAdmin)
16const testers = users.filter(u => u.isTester)
17const inactive = users.filter(u => !u.isActive)
18```
19 
20**Correct (1 iteration):**
21 
22```typescript
23const admins: User[] = []
24const testers: User[] = []
25const inactive: User[] = []
26 
27for (const user of users) {
28  if (user.isAdmin) admins.push(user)
29  if (user.isTester) testers.push(user)
30  if (!user.isActive) inactive.push(user)
31}
32```
33