js-combine-iterations

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):**

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

**Correct (1 iteration):**

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)
}