cocos creator2.0 計算兩點之間距離

cc.Class({
    extends: cc.Component,

    properties: {
    },

    onLoad: function () {
        this.startPos = cc.v2(0, 0);  //開始位置
        this.endPos = cc.v2(0, 0);    //結束位置

        this.node.on(cc.Node.EventType.TOUCH_START, function (event) {
            this.startPos = cc.v2(event.getLocation().x, event.getLocation().y);
            //獲取點擊的位置
            cc.log("起始坐標點：x = " + event.getLocation().x + ", y = " + event.getLocation().y);
        }, this);

        this.node.on(cc.Node.EventType.TOUCH_MOVE, function (event) {
            var delta = event.touch.getDelta();
            this.node.x += delta.x;
            this.node.y += delta.y;
        },this);


        this.node.on(cc.Node.EventType.TOUCH_END, function (event) {

            this.endPos = cc.v2(event.getLocation().x, event.getLocation().y);
            cc.log("終點坐標點 x ：" + event.getLocation().x + ", 終點坐標點 y ：" + event.getLocation().y );

            let distance = this.startPos.sub(this.endPos).mag();
            cc.log("移動距離 ：" + distance);
        }, this);

    },

    update: function (dt) {

    },
});