Day 9 of 100: Array Power Methods — map, filter, reduce, find

Day 9 of 100 — 100 Days of Playwright with TypeScript Challenge. Phase: JavaScript Fundamentals. JavaScript (Days 1-33) → TypeScript (Days 34-63) → Playwright (Days 64-96) → AI Framework Capstone (Days 97-100).

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map, filter, find, reduce, some, every — six methods that replace 80% of loops in test code.

The Big Six

const responses = [
  { url: '/users', status: 200, ms: 120 },
  { url: '/orders', status: 500, ms: 80 },
  { url: '/items', status: 200, ms: 450 },
];

// map — transform each
const urls = responses.map(r => r.url);

// filter — keep matching
const errors = responses.filter(r => r.status >= 400);

// find — first match
const slow = responses.find(r => r.ms > 400);

// some — at least one?
const hasErrors = responses.some(r => r.status >= 400); // true

// every — all match?
const allFast = responses.every(r => r.ms < 500);       // true

// reduce — accumulate
const totalMs = responses.reduce((sum, r) => sum + r.ms, 0); // 650

Chaining for Assertions

// 'Get names of all failing endpoints'
const failingUrls = responses
  .filter(r => r.status >= 400)
  .map(r => r.url);
// ['/orders']

// Real Playwright usage:
// const texts = await page.getByRole('listitem').allTextContents();
// const active = texts.filter(t => t.includes('Active'));

Tomorrow (Day 10): Objects — the shape of every API payload.