String.prototype.capitalize = function(capitalizeAll){
    if(capitalizeAll){
       return this.split(' ').map(function(e){return e.capitalize();}).join(' ');
    }else{
         return this.charAt(0).toUpperCase() + this.slice(1);
    }
};

"captitalize all words".capitalize(true); ==> "Captitalize All Words"
"capitalize just first word".capitalize(); ==> "Capitalize just first word"

Author: http://stackoverflow.com/a/20292655/703244