1.由宿主环境发起的称为宏观任务
2.由javascript引擎发起的称为微观任务
事件循环
宏观任务有：
| 浏览器 | node | |
|---|---|---|
| setTimeout | ✔️ | ✔️ |
| setInterval | ✔️ | ✔️ |
| setImmediate | ✘ | ✔️ |
| requestAnimationFrame | ✔️ | ✘ |
微观任务有：
| 浏览器 | node | |
|---|---|---|
| process.nextTick | ✘ | ✔️ |
| MutationObserver | ✔️ | ✘ |
| Promise | ✔️ | ✔️ |
setTimeout(()=>console.log(1));
const promise = new Promise((resolve, reject) => {
resolve()
console.log(2)
})
promise.then(() => {
console.log(3)
})
console.log(4);
//执行结果
//2
//4
//3
//1
