Promise

JavaScript是单线程指的是同一时间只能干一件事情，
所以想看到Promise执行前后的对比可以通过定时器完成。
Promise
Promise.then

const p1 = new Promise((resolve, reject) => {
    setTimeout(() => {
        resolve('成功');
    }, 10000);
})
const p2 = p1.then(() => {
    console.log('Promise执行resolve后');
    console.log(p1);
    console.log(p2);
}, () => {})
setTimeout(() => {
    console.log('Promise.then执行完成');
    console.log(p1);
    console.log(p2);
}, 10001);
console.log('Promise执行resolve前');
console.log(p1);
console.log(p2);

展开图