Capitalizing first letter of each word in string

JavaScript
2

I added comments, so hopefully this will explain everything…

function titleCase(str) {
     str = str.toLowerCase().split(' ');                // will split the string delimited by space into an array of words

     for(var i = 0; i < str.length; i++){               // str.length holds the number of occurrences of the array...
          str[i] = str[i].split('');                    // splits the array occurrence into an array of letters
          str[i][0] = str[i][0].toUpperCase();          // converts the first occurrence of the array to uppercase
          str[i] = str[i].join('');                     // converts the array of letters back into a word.
     }
     return str.join(' ');                              //  converts the array of words back to a sentence.
}
titleCase("I'm a little tea pot");

Personally, I’d use a little more memory and put it into different variables, but that’s just my opinion…

function titleCase(str) {
     words = str.toLowerCase().split(' ');

     for(var i = 0; i < words.length; i++) {
          var letters = words[i].split('');
          letters[0] = letters[0].toUpperCase();
          words[i] = letters.join('');
     }
     return words.join(' ');
}
titleCase("I'm a little tea pot");

Or better yet, use a regular expression, but my regEx ninja skills are VERY rusty, so I don’t want to lead you down that path…