JS Practice — Built-in Objects

Array.prototype.concat() — join two arrays

📖 Usage Example

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

Use concat() to merge two arrays into a new one without mutating either original.

Array.prototype.concat()

Array.prototype.concat() returns a new array that contains the elements of the original array followed by the elements of the provided arrays or values. The original arrays are not modified.

Challenge: Implement joinArrays(a, b) that returns a new array with all elements of a followed by all elements of b using .concat().

joinArrays([1, 2], [3, 4]) // → [1, 2, 3, 4]
joinArrays([], [1])        // → [1]

💡 Hints (2)

• `a.concat(b)` creates a new array — it never modifies `a` or `b`.
• You can also pass multiple arguments: `a.concat(b, c)` to concat more than two arrays.