Pattern: Callback on empty array slots
Issue: -
Using array methods with callbacks on arrays created with new Array(n) won't work as expected. Such arrays contain empty slots rather than actual values, so the callback is never invoked.
Example of incorrect code:
const items = new Array(3).map(i => i + 1);
const filled = new Array(5).forEach(console.log);Example of correct code:
const items = Array(3).fill().map(i => i + 1);
const filled = [...Array(5)].forEach(console.log);
const numbers = Array.from({length: 3}, (_, i) => i + 1);