javascript - Javascript 中的链表和对象错误

Question

我正在尝试 JS 及其各种库，但遇到了一个错误，我不太确定如何解释。相关代码如下:

function plotPoint (y, next, prev) {
    this.y = y;
    this.next = next;
    this.prev = prev;
}

function Fourier() {
    var self = this;
    self.init() = function() {
        ...
        self.firstPoint = new plotPoint(250, null, null);
        console.log(self.firstPoint); [1]
        ...
    }

    self.animate() = function() {
        ...
        console.log(self.firstPoint); [2]
        self.updatePlot();
        ...
    }

    self.updatePlot = function() {

        console.log(self.firstPoint); [3]

        //add new point to beginning
        var newPoint = new plotPoint(self.leadPoint.y, self.firstPoint, null);
        self.firstPoint.prev = newPoint
        self.firstPoint = self.newPoint;

        //remove last point from list, leave for collection
        self.lastPoint = self.lastPoint.prev;
        self.lastPoint.next = null;
    }
}

所有三个console.log结果都显示正确的对象，但后两个都伴随着“未定义”:

[1] plotPoint {y: 250, next: plotPoint, prev: null}
[2] plotPoint {y: 250, next: plotPoint, prev: null}
[3] plotPoint {y: 250, next: plotPoint, prev: null}
[2] undefined
[3] undefined

然后它会抛出错误“Uncaught TypeError: Cannot set property 'prev' of undefined”，引用 [3] 之后不久的行。

如果有帮助的话，该程序在没有包含在傅里叶类中时正在运行。我试图修改它，以便可以将它与 dat.GUI 一起使用。

预先感谢您的回复!

编辑:link到jsfiddle

Answer 1

对象self没有newPoint属性，因此它是未定义的。当您在第 106 行将 undefined 分配给 self.firstPoint 时，它也会变为 undefined。