Arrays, objects and destructuring

Test data is almost always arrays and objects. The most important array methods (all return a NEW array/value, leaving the original untouched):

• map — transform each element: users.map(u => u.email)
• filter — select matching ones: orders.filter(o => o.status === 'failed')
• find — first matching element (or undefined)
• some / every — does at least one / do all pass (boolean)
• includes — is a value in the array
• sort — CAREFUL: mutates the original and sorts as strings by default: [10, 2].sort() → [10, 2]; for numbers use sort((a, b) => a - b)

Destructuring — extracting values from objects/arrays in one line:

• const { id, email } = user;
• const [first, second] = rows;
• In function parameters: function login({ user, pass }) {...} — Playwright's async ({ page }) => {...} syntax is exactly this!

Spread (...) — copying and merging: const updated = { ...user, role: 'admin' } (a copy of user with role overridden). The core pattern for test data variations.

Optional chaining (?.) — safe deep access: response.data?.user?.email — returns undefined instead of throwing when an intermediate field is missing.