Flatten arrays of arbitrary depths, bringing all integers to top level

flatten_arrays_of_arbitrary_depths.js

'use strict';

function flatten(array) {
  let result = [];
  const f = function (x) {
    if (Array.isArray(x)) {
      x.forEach((x) => { f(x) });
    } else if (typeof x === 'number') {
      result.push(x)
    }
  };

  f(array);

  return result;
}

assert flatten([]) === []
assert flatten([[[[[[[[[[[[[[1]]]]]]]]]]]]]]) === [1]
assert flatten([[[3],[[[6,9]]]]]) === [3,6,9]
assert flatten([[4,5,'a','b'],[],[[[0]]]]) === [4,5,0]