javascript - 将带参数的方法添加到 javascript 对象

Question

我目前正在将我的一款 Java 小程序游戏移植到 javascript+html5。我以前从未做过面向对象的 JavaScript，这种基于原型(prototype)的 OO 东西让我很困惑。

我尝试从 java 进行简单的移植，但在做两件事时遇到困难:

1) 如何在构造函数内运行函数？
2) 如何添加带有参数的方法？

这里是一些示例代码:

function User()
{
    setupStats();// I wanted to put some of the variable initializations into
    // a separate function for code modularity reasons.

    this.name='bob';

    //However that doesn't seem to work
    alert(this.gold); // gets Undefined

    alert(this.name); // gets bob. Phew at least this works

    //I also want to add a method with a parameter in it:
    this.draw=function(ctx){drawUser(ctx);};
}

function setupStats()
{
    this.gold=2;
    this.exp=3;
    this.blah='blah';
    this.that='something else';
    this.superultraomg='insert some computation';
}

function drawUser(ctx)
{
    ctx.drawImage(blah,blah,blah);
    alert(ctx); // Also gets undefined. Uh oh...

    alert(this.name); //Undefined? WHAT IS THIS I DONT EVEN...
}

请大家帮忙!

Answer 1

Example

我们正在使用原型(prototype)，与所有用户共享setupStats中的默认值。我们正在使用 call传递一个上下文，即User对象和一个参数；

function User()
{
    setupStats();// I wanted to put some of the variable initializations into
    // a separate function for code modularity reasons.

    this.name='bob';

    //However that doesn't seem to work
    alert(this.gold); // gets Undefined

    alert(this.name); // gets bob. Phew at least this works

    //I also want to add a method with a parameter in it:
    this.draw= function(ctx){ drawUser.call(this, ctx); };
}

function setupStats()
{
    this.gold=2;
    this.exp=3;
    this.blah='blah';
    this.that='something else';
    this.superultraomg='insert some computation';
}

User.prototype = new setupStats();

new User().draw('pinky');

function drawUser(ctx)
{
    //ctx.drawImage(blah,blah,blah);
    alert(ctx); // Also gets undefined. Uh oh...

    alert(this.name); //Undefined? WHAT IS THIS I DONT EVEN...
}