JS flatt depth arrays

flattner

export const flattner = array => {
  if (!Array.isArray(array)) {
    throw Error(`${array} is not an Array`)
  }
  for (let i = 0; i < array.length;) {
   let value = array[i]
   if (Array.isArray(value)) {
     if (value.length > 0) {
       value.unshift(i, 1)
       array.splice.apply(array, value)
       value.splice(0, 2)
     } else {
       array.splice(i, 1)
     }
   } else {
     i++
   }
  }
  return array;
}

if (!flattner([1]) === [1]){
  throw Error(`Failure`)
}

if (!flattner([[1]]) === [1]){
  throw Error(`Failure`)
}

if (!flattner([1,[1]]) === [1,1]){
  throw Error(`Failure`)
}