JS Practice — Built-in Objects

Array.prototype.concat() — immutability

📖 Usage Example

const original = [1, 2, 3]
const extended = original.concat([4, 5])
// original → [1, 2, 3]  (unchanged)
// extended → [1, 2, 3, 4, 5]

concat() never mutates the original array — it always returns a new one.

Array.prototype.concat() — does not mutate

concat() always returns a new array. The original array is never modified. This makes it useful in functional programming and state management patterns.

Challenge: Implement safeConcat(arr, extra) that returns a new array combining arr and extra, without changing arr.

const original = [1, 2, 3]
safeConcat(original, [4, 5]) // → [1, 2, 3, 4, 5]
// original is still [1, 2, 3]

💡 Hints (2)

• `concat()` always returns a brand new array, leaving the original intact.
• This is one reason `concat` is preferred over `push` in immutable patterns like Redux reducers.