我觉得this.ctx.closePath();是多余的，不知老师为啥要闭合路径

        canvasLock.prototype.drawLine = function(po) {// 解锁轨迹
            this.ctx.beginPath();
            this.ctx.lineWidth = 3;
            this.ctx.moveTo(this.lastPoint[0].x, this.lastPoint[0].y);
            for (var i = 1 ; i < this.lastPoint.length ; i++) {
                this.ctx.lineTo(this.lastPoint[i].x, this.lastPoint[i].y);
            }
            this.ctx.lineTo(po.x, po.y);
            this.ctx.stroke();
            this.ctx.closePath();
        }
        canvasLock.prototype.drawPoint = function() { // 初始化圆心 
            for (var i = 0 ; i < this.lastPoint.length ; i++) {
                this.ctx.fillStyle = '#CFE6FF';
                this.ctx.beginPath();
                this.ctx.arc(this.lastPoint[i].x, this.lastPoint[i].y, this.r / 2, 0, Math.PI * 2, true);
                this.ctx.closePath();
                this.ctx.fill();
            }
        }

我粘贴的，出现了2次