In this article, we will use three approaches (First with a FOR loop, second using the sort() method, and third using the reduce() method) to Find the Longest Word in a Javascript String.

1. Find the Longest Word With a FOR Loop

We will use the String.prototype.split() method

• The split() method splits a String object into an array of strings by separating the string into sub strings.

We will need to add an empty space between the parenthesis of the split() method

var strSplit = “The quick brown fox jumped over the lazy dog”.split(‘ ‘);

which will output an array of separated words: strSplit = [“The”, “quick”, “brown”, “fox”, “jumped”, “over”, “the”, “lazy”, “dog”];

If you don’t add the space in the parenthesis, you will have this output:

var strSplit = [“T”, “h”, “e”, “ “, “q”, “u”, “i”, “c”, “k”, “ “, “b”, “r”, “o”, “w”, “n”, “ “, “f”, “o”, “x”, “ “, “j”, “u”, “m”, “p”, “e”, “d”, “ “, “o”, “v”, “e”, “r”, “ “, “t”, “h”, “e”, “ “, “l”, “a”, “z”, “y”, “ “, “d”, “o”, “g”];

Solution

function findLongestWord(str) {

            var strSplit = str.split(' ');

            var longestWord = 0;

            for (var i = 0; i < strSplit.length; i++) {

                if (strSplit[i].length > longestWord) {

                    longestWord = strSplit[i].length;

                }

            }

            return longestWord;

        }

findLongestWord("The quick brown fox jumped over the lazy dog");

2. Find the Longest Word With the sort() Method

For this solution, we will use the Array.prototype.sort() method to sort the array by some ordering criterion and then return the length of the first element of this array.

• The sort() method sorts the elements of an array in place and returns the array.

In our case, if we just sort the array

var sortArray = [“The”, “quick”, “brown”, “fox”, “jumped”, “over”, “the”, “lazy”, “dog”].sort();

we will have this output:

var sortArray = [“The”, “brown”, “dog”, “fox”, “jumped”, “lazy”, “over”, “quick”, “the”];

In Unicode, numbers come before upper case letters, which come before lower case letters.

We need to sort the elements by some ordering criterion,

[].sort(function(firstElement, secondElement) {     return secondElement.length — firstElement.length; })

where the length of the second element is compared to the length of the first element in the array.

function findLongestWord(str) {

var longestWord = str.split(' ').sort(function(a, b) { return b.length - a.length; });

  return longestWord[0].length;

}

findLongestWord("The quick brown fox jumped over the lazy dog");

3. Find the Longest Word With the reduce() Method

For this solution, we will use the Array.prototype.reduce().

• The reduce() method applies a function against an accumulator and each value of the array (from left-to-right) to reduce it to a single value.

reduce() executes a callback function once for each element present in the array.

You can provide an initial value as the second argument to reduce, here we will add an empty string “”.

[].reduce(function(previousValue, currentValue) {...}, “”);

function findLongestWord(str) {
  var longestWord = str.split(' ').reduce(function(longest, currentWord) {
    return currentWord.length > longest.length ? currentWord : longest;
  }, "");
  return longestWord.length;
}
findLongestWord("The quick brown fox jumped over the lazy dog");