JS Built-ins
← Array12 / 226
ArrayArray.frombeginner

Array.from() — create an index array

📖 Usage Example
Array.from({length: 3}, (_, i) => i)
// → [0, 1, 2]

Use Array.from() with an array-like object and a map function to generate index arrays.

Array.from() — length-object + map

Array.from() accepts any array-like object — including plain objects with a length property. Combined with the optional mapping function (second argument), you can generate sequences without a loop.

This pattern mirrors how Array.from(nodeList) works in the browser to convert a DOM NodeList into a real array.

Challenge: Implement createIndexArray that returns [0, 1, 2, …, n-1] using Array.from({ length: n }, (_, i) => i).

createIndexArray(3) // → [0, 1, 2]
createIndexArray(0) // → []
💡 Hints (2)
  • • `{ length: n }` is an array-like object — `Array.from` treats it like a sparse array.
  • • The mapping function receives `(value, index)` — use the index to produce the sequence.