Flattens Array

flatten.js

function* flatten(array, deep) {
  if (deep === undefined) deep = 1
  for (const item of array) {
    if (Array.isArray(item) && deep > 0) {
        yield* flatten(item, deep - 1)
    } else {
        yield item
    }
  }
}

// use case
const array = [[1,2,[3]],4]
const flattened = [...flatten(array, Infinity)] // Used Infinity, as if you're unsure of the depth (nested arrays)
console.log(flattened) // results [1,2,3,4]