测试题：Promise

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setTimeout(()=>{console.log(1)},0)
async function timeout (){
const a = await new Promise((res, rej) => {
setTimeout(() => {console.log(2); res(3)}, 0)
})
console.log(a);
}
await timeout();
console.log(4);

[smileyby]

setTimeout(()=>{
console.log(0)
}, 0);
new Promise((resolve, reject) => {
console.log(1);
resolve()
}).then(()=>{
console.log(2);
new Promise((resolve, reject) => {
console.log(3);
resolve();
}).then(() => {
console.log(4)
}).then(() => {
console.log(5)
})
}).then(() => {
console.log(6)
})

new Promise((resolve, reject) => {
console.log(7);
resolve();
}).then(() => {
console.log(8);
})

[smileyby]

https://jakearchibald.com/2015/tasks-microtasks-queues-and-schedules/

[smileyby]

Promise.prototype.then 方法，当未传入参数，或者参数非函数时，会被忽略掉且不会报错，当Promise状态发生改变的时候 then方法会将最后一次状态作为then的状态被执行