Converting to Arrays

You often need to convert array‑like objects or iterables into true arrays to use array methods. The most common ways are Array.from(), the spread operator (...), and Array.prototype.slice.call().

Key Points

• Array.from(arrayLike, mapFn) – converts and optionally maps.
• Spread operator [...arrayLike] – works on iterables.
• Array.prototype.slice.call(arrayLike) – old‑style conversion.

Code Example

// Array-like object
const arrayLike = { 0: "a", 1: "b", length: 2 };

// Method 1: Array.from
const arr1 = Array.from(arrayLike);
console.log(arr1); // ["a", "b"]

// With mapping function
const arrMapped = Array.from(arrayLike, (x) => x.toUpperCase());
console.log(arrMapped); // ["A", "B"]

// Method 2: Spread operator (requires iterable)
// For array-like, must be iterable (array-like are not iterable by default)
// But works on NodeList, arguments, etc.
const nodeList = document.querySelectorAll("div");
const arr2 = [...nodeList];

// Method 3: slice
const arr3 = Array.prototype.slice.call(arrayLike);
console.log(arr3); // ["a", "b"]