Recursively flatten a JS array

recursiveFlatten.js

function recursiveFlatten(array, ignoreObjects = false) {
  let current = []
  const arrayLength = array.length
  
  function isType(obj, type = 'Object') {
    return Object.prototype.toString.call(obj).indexOf(type) !== -1
  }

  for (let i = 0; i < arrayLength; i++) {
    let result
    if (ignoreObjects && isType(array[i], 'Object' /* could use typeof array[i] === 'object' */)) {
      continue
    } else if (isType(array[i], 'Array') /* could use Array.isArray(array[i]) */) {
      current = current.concat(recursiveFlatten(array[i]))
    } else {
      current.push(array[i])
    }
  }

  return current
}

// usage
const array = [[1, 2, 3], { a: 2 }, [4, 5, 'hello', [45, [67, 89, 78, [11, 22, 33]]]], [6, 7, 8, 9]]
console.log(recursiveFlatten(array))
// > [1, 2, 3, { a: 2 }, 4, 5, "hello", 45, 67, 89, 78, 11, 22, 33, 6, 7, 8, 9]
console.log(recursiveFlatten(array, true))
// > [1, 2, 3, 4, 5, "hello", 45, 67, 89, 78, 11, 22, 33, 6, 7, 8, 9]