How to tell if one string is one edit away from another string in JavaScript

JavaScript, algorithms, strings

Here is one way to tell if a string is one edit (insertion, removal, modification) from another string in JavaScript.
Space complexity: O(1)
Time complexity: O(n) to iterate through n characters

oneAwayTry in REPL
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function oneAway(string1, string2) {
  if (string1.length - string2.length > 1) return false;
  let numDiff = 0;
  
  if (string1.length === string2.length) {
    for (let i = 0; i < string1.length; i++) {
      const char1 = string1[i];
      const char2 = string2[i];
      if (char1 !== char2) numDiff++;
    }
  } else {
    for (let i = 0, j = 0; i < Math.max(string1.length, string2.length) && j < Math.max(string1.length, string2.length); i++, j++) {
      if (string1[i] !== string2[j]) {
        numDiff++;
        if (numDiff > 1) return false;
        (string1.length > string2.length && i++) || j++;
      }
      const char1 = string1[i];
      const char2 = string2[j];
      if (char1 !== char2) numDiff++;
    }
  }
  return numDiff <= 1;
}

Test cases can be found at REPL.it