Find the longest word in a sentence and return word length (JavaScript)

findLongestWord.js

function findLongestWord(str) {

  var splitString = str.split(" ");
  var longestString = splitString[0];

  for (var i = 0; i < splitString.length; i++) {
    if (splitString[i].length > longestString.length) {
      longestString = splitString[i];
    }
  }
  return longestString.length;
}