/**
 * 船
 */
class Boat extends Laya.Sprite {
    private bt:Laya.Sprite;
    constructor() {
        super()
        this.bt = new Laya.Sprite()
        this.bt.loadImage("res/boat.png")
        this.addChild(this.bt)
    }
}

/**
 * 游戏背景
 */

class BackGround extends Laya.Sprite {
    //背景图
    private bg:Laya.Sprite;

    constructor(){
        super();
        this.init();
    }

    init():void{
        this.bg = new Laya.Sprite()
        this.bg.loadImage("res/background.png")
        this.addChild(this.bg)
    }
}

/**
* Game
*/
class Game {
  
    constructor(){
        Laya.init(768,1136);

        //设置适配模式
        Laya.stage.scaleMode = "showall";
        //设置剧中对齐
        Laya.stage.alignH = "center";
        //设置横竖屏
        Laya.stage.screenMode = "vertical";
        //创建背景
        let bg:BackGround = new BackGround();
        
        Laya.stage.addChild(bg);
        //创建船
        let bt:Boat = new Boat();
        Laya.stage.addChild(bt)

         //获取动画大小区域
        var bgBound: Laya.Rectangle = bg.getBounds();
        var btBound: Laya.Rectangle = bg.getBounds();


        console.log(bgBound.width/2)
        console.log(bgBound.height - 150)
        bt.pos(bgBound.width/2 - btBound.width/2,bgBound.height - 150)
    }

    
}
  
//启动游戏
new Game();

打印结果：
0
-150
bgBound.width 和 bgBound.heigt 都为0