// promise.all
function promiseAll(promisesArr) {
return new Promise((resolve, reject) => {
// 定义一个计数器
let count = 0;
const arr = [];
const l = promisesArr.length;
let startTime = new Date().getTime();
for (let i = 0; i < l; i++) {
promisesArr[i]
.then((res) => {
count++;
// arr.push(res); 这里不能直接 push ,因为要保证 顺序
arr[i] = res;
if (count === l) {
resolve(arr);
let endTime = new Date().getTime();
console.log(endTime - startTime); // 耗费的总时长为最长的 promise 时长
}
})
.catch((err) => {
// console.log(err);
reject(err);
});
}
});
}
const promiseA = new Promise((resolve, reject) => {
resolve("A");
});
const promiseB = new Promise((resolve, reject) => {
reject("B error");
// resolve("B");
});
promiseAll([promiseA, promiseB])
.then((res) => {
console.log(res);
})
.catch((err) => {
console.log(err);
});
let wake = (time) => {
return new Promise((resolve, reject) => {
setTimeout(() => {
resolve(`${time / 1000}秒后醒来`);
}, time);
});
};
let p1 = wake(3000);
let p2 = wake(2000);
Promise.all([p1, p2])
.then((result) => {
console.log(result); // [ '3秒后醒来', '2秒后醒来' ] 按照顺序输出
})
.catch((error) => {
console.log(error);
});
promiseAll([p1, p2])
.then((res) => {
console.log(res);
})
.catch((err) => {
console.log(err);
});
// Promise.race
// Promse.race就是赛跑的意思,意思就是说,Promise.race([p1, p2, p3])里面哪个结果获得的快,就返回那个结果,不管结果本身是成功状态还是失败状态。
let p11 = new Promise((resolve, reject) => {
setTimeout(() => {
resolve("success");
}, 1000);
});
let p22 = new Promise((resolve, reject) => {
setTimeout(() => {
reject("failed");
}, 500);
});
Promise.race([p11, p22])
.then((result) => {
console.log(result);
})
.catch((error) => {
console.log(error); //'failed'
});
function promiseRace(promiseArr) {
return new Promise((resolve, reject) => {
for (let i = 0; i < promiseArr.length; i++) {
promiseArr[i]
.then((res) => {
resolve(res);
})
.catch((err) => {
reject(err);
});
}
});
}
promiseRace([p11, p22])
.then((res) => {
console.log(res);
})
.catch((err) => {
console.log(err);
});//'failed'
学习链接:https://www.jianshu.com/p/7e60fc1be1b2