Array-like objects

Model answer. An array-like object has numbered keys and a length property, but is not an Array, so it lacks methods like map and filter.

Common examples:

• arguments inside a non-arrow function
• a DOM NodeList from querySelectorAll (modern ones do have forEach, but not map)
• an HTMLCollection from getElementsByClassName
• strings (indexed characters with a length)

Converting:

const items = document.querySelectorAll('li');
const arr1 = Array.from(items);            // works for array-likes and iterables
const arr2 = [...items];                   // works for iterables only
const texts = Array.from(items, li => li.textContent);  // convert + map in one step

Array.from is the safest choice because it accepts plain { length, 0:..., 1:... } objects too, which spread does not (they are not iterable).