if (deltaTime>40) deltaTime=40;  为什么这段代码放在gameloop()的尾端就没用了呢

function gameloop(){

window.requestAnimFrame(gameloop);

var now=Date.now();

deltaTime=now-lastTime;

lastTime=now;

fruitMonitor();

    background();

ane.draw();

fruit.draw();

ctx1.clearRect(0,0,canWidth,canHeight)

mom.draw();

momFruitCollision();

if (deltaTime>40) deltaTime=40;

}