javascript - setTimeout 只运行一次

Question

我正在尝试向 cleatRect 函数添加延迟，我的目标是让动画 Sprite 创建“拖尾效果”，但是，仅 setTimeout 函数当 Canvas 动画开始时运行一次。我是否遗漏了一些明显的东西？

var draw = function() { // draw loop 
    setTimeout(function() { // this runs once
        ctx.clearRect(0, 0, 700, 560);
    }, 2000);

    ctx.drawImage(sprites.background, bkg.x, bkg.y);
    aliens.forEach(function(element, index) {
        ctx.drawImage(sprites.enemy, element.clipX, element.clipY, element.w, element.h, element.x, element.y, element.w, element.h);
    });
};

Answer 1

setTimeout

Sets a timer which executes a function or specified piece of code once after the timer expires.

您想要:setInterval

Repeatedly calls a function or executes a code snippet, with a fixed time delay between each call. Returns an intervalID.