coding problem - binary search function in JS, with comments

binsearch.js

function binary_search(x, sorted_collection, low = 0, high = null) {
  // x is target
  // sorted_collection I will assume is always sorted in ascending numerical order AND starting from 1
  // low is the start index
  // high is the end index
  if (high === null) {
    high = sorted_collection.length; // using .length will return 1 index higher as arrays start with a 0 index, not 1
  } else if (high < 0) {
    throw new RangeError("High index out of range");
  }

  if (low > high) return null;

  const mid = Math.floor((high + low) / 2);
  const value = sorted_collection[mid];

  if (value == x) {
    // loose equality check here, checks whether its two operands are equal e.g. '1' == 1 will output true. See https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Operators/Equality
    // rather than strict equality which will try to convert and then compare the operands e.g. '1' === 1 will output false. See https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Operators/Strict_equality
    return value; // value is the actual value at sorted_collection[mid], not the index itself
  } else if (value > x) {
    // if middle value is greater than target value of x, we should search left using middle as ending index
    return binary_search(x, sorted_collection, mid + 1, high);
  } else {
    // if target value is not inside the sorted_collection, we will trigger the conditional on line 8 & then throw the error on line 9
    return binary_search(x, sorted_collection, low, mid - 1);
  }
}

// Don't change anything below this line ;)

const tests = [
  {
    find: 1,
    collection: [],
    expected: null,
  },
  {
    find: 1,
    collection: [1],
    expected: 0,
  },
  {
    find: 2,
    collection: [1],
    expected: null,
  },
  {
    find: 1,
    collection: [1, 2],
    expected: 0,
  },
  {
    find: 2,
    collection: [1, 2],
    expected: 1,
  },
  {
    find: 3,
    collection: [1, 2, 3],
    expected: 2,
  },
  {
    find: 1,
    collection: [1, 2, 3, 4],
    expected: 0,
  },
  {
    find: 2,
    collection: [1, 2, 3, 4],
    expected: 1,
  },
  {
    find: 3,
    collection: [1, 2, 3, 4],
    expected: 2,
  },
  {
    find: 4,
    collection: [1, 2, 3, 4],
    expected: 3,
  },
  {
    find: 1,
    collection: [1, 2, 3, 4, 5],
    expected: 0,
  },
  {
    find: 2,
    collection: [1, 2, 3, 4, 5],
    expected: 1,
  },
  {
    find: 3,
    collection: [1, 2, 3, 4, 5],
    expected: 2,
  },
  {
    find: 4,
    collection: [1, 2, 3, 4, 5],
    expected: 3,
  },
  {
    find: 5,
    collection: [1, 2, 3, 4, 5],
    expected: 4,
  },
  {
    find: 99,
    collection: [1, 2, 3, 4, 5],
    expected: null,
  },
];

const results = tests.map(function (test) {
  try {
    var result = binary_search(test["find"], test["collection"]);
    test.result = result;
    test.success = result == test["expected"];
  } catch (ex) {
    test.result = ex.message;
    test.success = false;
  }

  return test;
});

console.table(results);