JS Practice — Built-in Objects

Array.prototype.concat() — merge three arrays

📖 Usage Example

const a = [1, [2, 3]]
const b = [[4], 5]
a.concat(b)  // → [1, [2, 3], [4], 5]

concat() appends array elements at one level — nested arrays are NOT flattened.

Array.prototype.concat() — chaining multiple arrays

You can pass multiple arrays to a single concat() call. This merges them all without intermediate arrays.

Challenge: Implement mergeThree(a, b, c) that returns a single array containing all elements from a, b, and c using a.concat(b, c).

mergeThree([1], [2, 3], [4]) // → [1, 2, 3, 4]
mergeThree([], ['x'], ['y']) // → ['x', 'y']

💡 Hints (2)