javascript - 如何将这段 Python 翻译成地道的 Javascript

Question

到目前为止我的代码:

// The q constant of the Glicko system.
var q = Math.log(10) / 400;

function Player(rating, rd) {
    this.rating = rating || 1500;
    this.rd = rd || 200;
}

Player.prototype.preRatingRD = function(this, t, c) {
    // Set default values of t and c
    this.t = t || 1;
    this.c = c || 63.2;
    // Calculate the new rating deviation
    this.rd = Math.sqrt(Math.pow(this.rd, 2) + (Math.pow(c, 2) * t));
    // Ensure RD doesn't rise above that of an unrated player
    this.rd = Math.min(this.rd, 350);
    // Ensure RD doesn't drop too low so that rating can still change
    // appreciably
    this.rd = Math.max(this.rd, 30);
};
Player.prototype.g = function(this, rd) {
    return 1 / Math.sqrt(1 + 3 * Math.pow(q, 2) * Math.pow(rd, 2) / Math.pow(Math.PI, 2));
};
Player.prototype.e = function(this, p2rating, p2rd) {
    return 1 / (1 + Math.pow(10, (-1 * this.g(p2rd) * (this.rating - p2rating) / 400)));
};

我正在研究 Glicko rating system 的 JS/HTML 实现并大量借用 pyglicko -- 也就是说，完全扯掉它。

它相当短(可能少于 100 LoC，没有评论)但我对我的翻译是否有效感到疑虑，因为老实说，我不知道 Javascript 作用域和 this 实际上是如何工作的。您可以在顶部的链接中看到我的内容。

但具体来说，我想知道您将如何用 Javascript 表达这段 Python 代码。基本上 _d2 在 Player 的类定义中。

def _d2(self, rating_list, RD_list):
    tempSum = 0
    for i in range(len(rating_list)):
        tempE = self._E(rating_list[i], RD_list[i])
        tempSum += math.pow(self._g(RD_list[1]), 2) * tempE * (1 - tempE)
    return 1 / (math.pow(self._q, 2) * tempSum)

我已经像这样定义了函数 e 和 g，并且 q 是一个常量:

Player.prototype.e = function(this, ratingList, rdList) {
    // Stuff goes here
}

Answer 1

在 Javascript 中，您不需要显式传递 self(实际上，Python 是这里的“怪异”对象)

Player.prototype.e = function(rating_list, RD_list){
    //replace "self" with "this" here:
    var tempSum = 0; //if you don't use the "var", tempSum will be a global
                     // instead of a local
    for(var i=0; i<rating_list.length; i++){ //plain old for loop - no foreach in JS
        var tempE = this._E( ... ); //note that in JS, just like in Python,
                                    //variables like this have function scope and
                                    //can be accessed outside the loop as well
        tempSum += Math.pow( ... ) //the Math namespace is always available
                                   //Javascript doesn't have a native module system
    }
    return (...);
}

这应该没问题。 关于 this，您需要了解的唯一棘手的事情是它非常混杂。这意味着这取决于您调用函数的方式:

 obj.e(); //if you do a method-like call, the this will be set to obj

然而，幕后并没有魔法绑定(bind)。以下在 python 中有效，但在 Javascript 中不有效:

 f = obj.e
 f(); //looks like a normal function call. This doesn't point to obj