Partition an array into 2 arrays in TypeScript

partition.ts

interface IPartitionFunction<T> {
  (element: T): boolean;
}

/**
 * Partitions an array in to two arrays based on `isValid` function
 * @param array Array to partition
 * @param isValid Function to test each item against
 */
const partition = <T>(array: T[], isValid: IPartitionFunction<T>): T[][] => {
  return array.reduce(([pass, fail]: T[][], elem) => {
    return isValid(elem) ? [[...pass, elem], fail] : [pass, [...fail, elem]];
  }, [[], []]);
};
  
// Examples

const array = [1, 5, 32, 6, 2, 642, 62, 4];
const [pass, fail] = partition(array, item => item < 20);

console.log('pass', pass);
// pass [ 1, 5, 6, 2, 4 ]
console.log('fail', fail);
// fail [ 32, 642, 62 ]

const objectArray = [
  {
    key: 'key1',
    value: 1
  }, {
    key: 'key2',
    value: 5
  }, {
    key: 'key1',
    value: 32
  }, {
    key: 'key1',
    value: 78
  }, {
    key: 'key1',
    value: 2
  }, {
    key: 'key1',
    value: 642
  }, {
    key: 'key1',
    value: 62
  }, {
    key: 'key1',
    value: 4
  }
];
                                                         
const [passItems, failItems] = partition(objectArray, item => item.value < 15);

console.log('pass', passItems);
// pass [ { key: 'key1', value: 1 },
//   { key: 'key2', value: 5 },
//   { key: 'key5', value: 2 },
//   { key: 'key8', value: 4 } ]
console.log('fail', failItems);
// fail [ { key: 'key3', value: 32 },
//   { key: 'key4', value: 78 },
//   { key: 'key6', value: 642 },
//   { key: 'key7', value: 62 } ]