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