如何把一句英文每个单词首字母大写？

 //面试题：如何把一句英文每个单词首字母大写？
                var str="what fuck is 1235 going on ?";
                var arr=str.split(" ");
                for(var i=0,newArr=[],sumArr=[];i<arr.length;i++){
                     var news=arr[i][0].toUpperCase();
                     newArr.push(news);
                     var sums=arr[i].slice(1);
                     sumArr.push(sums);
                     arr[i]=newArr[i]+sumArr[i];
                }
                 str=arr.join(" ");
                 console.log(arr,str);//["What", "Fuck", "Is", "1235", "Going", "On", "?"] "What Fuck Is 1235 Going On ?"