一道面試題

function xu(name){
  if(name)
    this.name=name;
}
function xu2(name){
  this.name = name || "bin";
}
function xu3(name){
  this.name = name;
}

xu.prototype.name = "xu";
xu2.prototype.name = "xu2";
xu3.prototype.name = "xu3";

console.log((new xu().name)+(new xu2().name)+(new xu3().name));