1、代码输出结果
const promise = new Promise((resolve, reject) => {
console.log(1);
console.log(2);
});
promise.then(() => {
console.log(3);
});
console.log(4);
2、代码输出结果
const promise1 = new Promise((resolve, reject) => {
console.log('promise1')
resolve('resolve1')
})
const promise2 = promise1.then(res => {
console.log(res)
})
console.log('1', promise1);
console.log('2', promise2);
3、代码输出结果
const promise = new Promise((resolve, reject) => {
console.log(1);
setTimeout(() => {
console.log("timerStart");
resolve("success");
console.log("timerEnd");
}, 0);
console.log(2);
});
promise.then((res) => {
console.log(res);
});
console.log(4);
4、代码输出结果
Promise.resolve().then(() => {
console.log('promise1');
const timer2 = setTimeout(() => {
console.log('timer2')
}, 0)
});
const timer1 = setTimeout(() => {
console.log('timer1')
Promise.resolve().then(() => {
console.log('promise2')
})
}, 0)
console.log('start');
5、代码输出结果
const promise = new Promise((resolve, reject) => {
resolve('success1');
reject('error');
resolve('success2');
});
promise.then((res) => {
console.log('then:', res);
}).catch((err) => {
console.log('catch:', err);
})
6、代码输出结果
Promise.resolve(1)
.then(2)
.then(Promise.resolve(3))
.then(console.log)
7、代码输出结果
const promise1 = new Promise((resolve, reject) => {
setTimeout(() => {
resolve('success')
}, 1000)
})
const promise2 = promise1.then(() => {
throw new Error('error!!!')
})
console.log('promise1', promise1)
console.log('promise2', promise2)
setTimeout(() => {
console.log('promise1', promise1)
console.log('promise2', promise2)
}, 2000)
8、代码输出结果
Promise.resolve(1)
.then(res => {
console.log(res);
return 2;
})
.catch(err => {
return 3;
})
.then(res => {
console.log(res);
});
9、代码输出结果
Promise.resolve().then(() => {
return new Error('error!!!')
}).then(res => {
console.log("then: ", res)
}).catch(err => {
console.log("catch: ", err)
})
10、代码输出结果
const promise = Promise.resolve().then(() => {
return promise;
})
promise.catch(console.err)
tips:
1、代码从上往下，顺序执行，先同步，后异步
2、
setTimeout是一个宏任务3、
Promise.resolve().then是一个微任务
