var fade = function (node) {
var level = 1;
var step = function () {
var hex = level.toString(16);
node.style.backgroundColor = "#FFFF" + hex + hex;
if(level < 15) {
level += 1;
setTimeout(step, 100);
}
};
setTimeout(step, 100);
};
fade(document.body);定义一个函数，它设置一个DOM节点为黄色，然后把它渐变为白色
![[Web front-end] Node.js quick start](https://img.php.cn/upload/course/000/000/067/662b5d34ba7c0227.png)
Why are there two setTimeouts and what do they mean? -PHP Chinese website Q&A-Why are there two setTimeouts and what do they mean? -PHP Chinese website Q&A
Let’s take a look and learn.
setTimeout只是延时一次, 所以最底下那个，是初始时的延迟，然后执行step函数，然后level还没到15，所以level+1,然后执行setTimeout，然后在level还没达到15之前，一直在调用setTimeout延迟调用step函数，直到最后一次setTimeout执行step时，level=15了，不再执行if条件下的内容~