bifurcateBy

Splits values into two groups, based on the result of the given filtering function.

• Use Array.prototype.reduce() and Array.prototype.push() to add elements to groups, based on the value returned by fn for each element.
• If fn returns a truthy value for any element, add it to the first group, otherwise add it to the second group.

const bifurcateBy = (arr, fn) =>
  arr.reduce((acc, val, i) => (acc[fn(val, i) ? 0 : 1].push(val), acc), [
    [],
    [],
  ]);

bifurcateBy(['beep', 'boop', 'foo', 'bar'], x => x[0] === 'b');
// [ ['beep', 'boop', 'bar'], ['foo'] ]