控制台说我创建的功能不存在

Question

当我运行此代码时：

//Function to see if a line is colliding with a certain point Has an accuracy of about 1 pixel
    this.lineIsColliding = function(startX, startY, endX, endY, testX, testY) {
        const v1 = {
            x: endX - startX,
            y: endY - startY
        };
        const l2 = v1.x * v1.x + v1.y * v1.y;
        if (l2 === 0) {
            return false;
        } // line has no length so can't be near anything
        const v2 = {
            x: testX - startX,
            y: testY - startY
        };
        const u = (v1.x * v2.x + v1.y * v2.y) / l2;
        return u >= 0 && u <= 1 && Math.abs((v1.x * v2.y - v1.y * v2.x) / Math.sqrt(l2)) < 1;
    };

    //The Canvas to draw on
    this.src = src;
    //The context of source(used for drawing)
    this.ctx = this.src.getContext("2d");
    //The Mouse Move Function
    this.showCoordinates = function(e) {
        console.log(e);
        label.innerHTML = "<b>x: </b>" + e.offsetX + " <b>y: </b>" + e.offsetY + ", " + this.lineIsColliding(358, 277, 365, 268, e.offsetX, e.offsetY);
    };

（不是整个代码。剪断只显示重要部分）

控制台说我的lineIsColliding功能不存在！这正是它所说的： 未捕获的TypeError：this.lineIsColliding不是函数

Answer 1

那是因为 this 指的是小功能范围内的 this 。使用var self = this;在较高的范围内。

然后再次调用该函数：

self.lineIsColliding(358, 277, 365, 268, e.offsetX, e.offsetY);