输出语句末尾的 Javascript 对象未定义关键字

Question

我在 javascript 中创建了一个运行良好的对象，但在每个语句的末尾都显示“未定义”。这是我的 javascript。

<script>
    window.onload=function(){
        function sports(sportsname, country, player, difficulty){
             this.sportsname = sportsname;
             this.country = country;
             this.player = player;
             this.difficulty = difficulty; 
             this.hissportstaste = sportstaste;
        }

        var Cricket = new sports("Cricket", "Pakistan", "Shahid Afridi", "Difficult");
        var Football = new sports("Football", "Spain", "David Villa", "Difficult");
        var Tennis = new sports("Tennis", "Switzerland", "Roger Federer", "Difficult");

        function sportstaste(){
            if(this.country == "Pakistan"){
                document.write(this.player + " Is the best and he is a " + this.sportsname + " Player");
            }
            if(this.country == "Spain"){
                document.write(this.player + " Is the best and he is a " + this.sportsname + " Player");
            }
            if(this.country == "Switzerland"){
                document.write(this.player + " Is the best and he is a " + this.sportsname + " Player");
            }
        }
        document.write(Cricket.hissportstaste());
        document.write("<br>");
        document.write(Football.hissportstaste());
        document.write("<br>");
        document.write(Tennis.hissportstaste());
        document.write("<br>");
    }

    </script> 

及其给出的输出是。

Shahid Afridi Is the best and he is a Cricket Playerundefined
David Villa Is the best and he is a Football Playerundefined
Roger Federer Is the best and he is a Tennis Playerundefined

我期待这个输出。

Shahid Afridi Is the best and he is a Cricket Player
David Villa Is the best and he is a Football Player
Roger Federer Is the best and he is a Tennis Player

有什么想法吗？？

Answer 1

改变

document.write(Football.hissportstaste());

到

Football.hissportstaste();

对于类似的调用也是如此:您的函数不返回任何内容(undefined)并且已经写入文档。

但是你应该尽量避免document.write，这个函数有非常特殊的用途(it can't be used once the document is loaded)，你应该学会改变DOM(参见this例如)。