binarySearch.js

test('binary search returns true if the value exists in middle', t => {
  const list = [1, 2, 3, 4, 5, 6, 7];
  const target = 4;

  t.is(binarySearch(list, target), 4);
});

test('binary search returns true if the value exists in upper half', t => {
  const list = [1, 2, 3, 4, 5, 6, 7];
  const target = 6;

  t.is(binarySearch(list, target), 6);
});

test('binary search returns true if the value exists in lower half', t => {
  const list = [1, 2, 3, 4, 5, 6, 7];
  const target = 3;

  t.is(binarySearch(list, target), 3);
});

const binarySearch = (list, target) => {
  const midpoint = Math.floor(list.length / 2);
  
  if (list[midpoint] === target) {
    return list[midpoint];
  } else if (list[midpoint] < target && list.length > 1) {
    return binarySearch(list.splice(midpoint, Number.MAX_VALUE), target);
  } else if (list[midpoint] > target && list.length > target) {
    return binarySearch(list.splice(0, midpoint), target);
  } else {
    return -1;
  }
};