String prototype一个 小字符串方法，感觉他挺好的，原型链是个好东西

var a = "dragon {num},{age}";
var b = "dragon {0},{1}";

String.prototype.format = function (){
var str = this.toString();
if(typeof arguments[0] === "object"){
for(i in arguments[0]){
str = str.replace("{"+i+"}",arguments[0][i]);
}
}else{
for(var i=0; i<arguments.length; i++){
str = str.replace("{"+i+"}",arguments[i])
}
}

return str;
};

console.log(a.format({num:10,age:100}));
console.log(b.format('10','100'));