JS Practice — Built-in Objects

Array.prototype.flatMap() — expand ranges

📖 Usage Example

const ranges = [2, 3]
ranges.flatMap(n => Array.from({length: n}, (_, i) => i))
// → [0, 1, 0, 1, 2]

Use flatMap() to expand each element into a sequence of values.

Array.prototype.flatMap() — generating sequences

flatMap() can expand each element into multiple elements. For example, each [start, end] pair can be expanded into the full range.

Challenge: Implement expandRange(pairs) where each [start, end] pair expands to [start, start+1, ..., end].

expandRange([[1, 3], [6, 8]]) // → [1, 2, 3, 6, 7, 8]
expandRange([[5, 5]])         // → [5]

💡 Hints (2)

• `Array.from({ length: end - start + 1 }, (_, i) => start + i)` generates the range sequence.
• `flatMap` then flattens all these range arrays into one.