js 宏任务与微任务总结

宏任务macrotask有哪些

script setTimeout setInterval setImmediate requestAnimationFrame I/O操作 UI渲染

微任务microtask有哪些

process.nextTick MutationObserver Promise.then

执行优先级

主线程script>
微任务process.nextTick>promise>
宏任务setTimeout>setInterval>setImmediate>I/O>UI rendering

I/O是什么

mouse click , keypresses, network events

js内部执行机制

主线程script执行完=> 执行所有微任务=> 执行栈中第一个宏任务=> 执行所有微任务=> 执行栈中第一个宏任务=>…

举个例子，打印顺序就是数字顺序：

setTimeout(() => console.log(2), 0);
setTimeout(() => {
  console.log(3);
  Promise.resolve().then(() => {
    console.log(4);
    Promise.resolve().then(() => {
      console.log(6);
    });
    console.log(5)
  });
  setTimeout(() => console.log(8), 0);
}, 0);
setTimeout(() => console.log(7), 0);
Promise.resolve().then(() => {
  console.log(1);
});
//process.nextTick(()=>console.log(0)); //浏览器环境注释此句

关注下再走呗 +_+