function longestWord(string) { var str = string.split(\" \"); var longest = 0; var word = null; for (var i = 0; i < str.length - 1; i++) {
You have a -1 in your condition, it never even scans it:
-1
for (var i = 0; i < str.length - 1; i++) {
Should be:
for (var i = 0; i < str.length; i++) {
Demo: http://jsfiddle.net/LfgFk/