字符串处理

1.传入一个string类型的参数，然后将string的每个字符间加个空格返回

   String.prototype.spacify = function(){
       return this.split("").join(" ");
   };
   console.log("abc".spacify()); //a b c

2.将数组[1,2,3,4,5]变为[1,2,3,4,5,1,2,3,4,5]

   Array.prototype.duplicator = function(){
       return this.concat(this);7    
   console.log([1,2,3,4,5].duplicator()); //[1,2,3,4,5,1,2,3,4,5]

3.输出参数，且加上规定的前缀

   function log(){
       var str = Array.prototype.slice.call(arguments);
       str.unshift("(app)");
       console.log.apply(console,str);
   }
   log("hello","world");  //(app) hello world

 4.接收一个整数作为字符串重复的次数，返回重复的字符串

  String.prototype.repeatify = String.prototype.repeatify || function (num){
       var str = "";
       for (var i = 0; i < num; i++){
           str +=this;
       }
       return str;
   };
   console.log("hello".repeatify(3));  //hellohellohello

 5.变为驼峰式

  var foo = "get-element-by-id";
   function como(str){
       var arr = str.split("-");
       var elem;
       var newArr = [arr[0]];
       for(var i =1,len = arr.length; i < len; i++){
           elem = arr[i];
           elem = elem.charAt(0).toUpperCase()+elem.slice(1,elem.length);
           newArr.push(elem);
       }
       return newArr.join("");
   }
   console.log(como(foo));  //getElementById