String is subsequence algorithm in JavaScript

Given two strings needle and haystack, check if needle is a subsequence (not necessarily a substring) of haystack at any point. That means that the letters in needle must appear in haystack in the same order, but not necessarily contiguously.

function isSubsequence(needle, haystack) {
  if (!needle) {
    return true;
  }
  if (haystack.length < needle.length) {
    return true;
  }
  if (haystack === needle) {
    return true;
  }
  let ni = 0;
  let hi = 0;
  while (hi < haystack.length) {
    if (haystack[hi] === needle[ni]) {
      ni++;
    }
    if (ni === needle.length) {
      return true;
    }
    hi++;
  }
  return false;
}

This algorithm has $O(m+n)$ time complexity and $O(1)$ space complexity.

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