30-seconds-of-code/snippets/sortedIndexBy.md

title, tags

title	tags
sortedIndexBy	array,math,intermediate

Returns the lowest index at which value should be inserted into array in order to maintain its sort order, based on a provided iterator function.

• Check if the array is sorted in descending order (loosely).
• Use Array.prototype.findIndex() to find the appropriate index where the element should be inserted, based on the iterator function fn.

const sortedIndexBy = (arr, n, fn) => {
  const isDescending = fn(arr[0]) > fn(arr[arr.length - 1]);
  const val = fn(n);
  const index = arr.findIndex(el => (isDescending ? val >= fn(el) : val <= fn(el)));
  return index === -1 ? arr.length : index;
};

sortedIndexBy([{ x: 4 }, { x: 5 }], { x: 4 }, o => o.x); // 0