1//capitalize only the first letter of the string. 
2function capitalizeFirstLetter(string) {
3    return string.charAt(0).toUpperCase() + string.slice(1);
4}
5//capitalize all words of a string. 
6function capitalizeWords(string) {
7    return string.replace(/(?:^|\s)\S/g, function(a) { return a.toUpperCase(); });
8};

1var str = "Hello World!";
2var res = str.toUpperCase();  //HELLO WORLD!

1function toTitleCase(str) {
2    return str.replace(/\w\S*/g, function(txt){
3        return txt.charAt(0).toUpperCase() + txt.substr(1).toLowerCase();
4    });
5}

1//Updated 
2//capitalize only the first letter of the string. 
3function capitalizeFirstLetter(string) {
4    return string.charAt(0).toUpperCase() + string.slice(1);
5}
6//capitalize all words of a string. 
7function capitalizeWords(string) {
8    return string.replace(/(?:^|\s)\S/g, function(a) { return a.toUpperCase(); });
9};