Flatten Arrays

flatten-array.js

function flatten(arr) {
  return arr.reduce(function (acc, item) {
		if (item instanceof Array) {
    	return acc.concat(flatten(item))
    } else {
    	return acc.concat(item)
    } 
  }, []);
}

const myArr = [[1, 2, 3], 4, [5, [6]], [[[[[[8]]]]]]];
console.log(flatten(myArr));