JS Practice — Built-in Objects

Array.prototype.reduce() — flatten nested arrays

📖 Usage Example

const nested = [[1, 2], [3, 4], [5]]
nested.reduce((acc, arr) => acc.concat(arr), [])
// → [1, 2, 3, 4, 5]

Use reduce() to flatten one level of nested arrays by concatenating each sub-array.

Flattening with reduce + concat

You can flatten a 2D array using reduce() with concat().

[[1, 2], [3, 4]].reduce((acc, cur) => acc.concat(cur), []) // [1, 2, 3, 4]

💡 Hints (3)