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60 lines (54 loc) · 1.5 KB
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/*
* @Author: yewei
* @Date: 2021-08-13 11:43:15
* @Last Modified by: yewei
* @Last Modified time: 2021-08-13 15:01:59
*
* 实现Promise.all方法
*
* 1. 接收可迭代对象
* 2. 判断可迭代对象是否为空，如果为空，直接返回Promise.resolve([])
* 3. 当所有 Promise 完成时，resolve 一个结果数组
* 4. 当其中有一个失败，立刻 reject
*/
const promiseAll = (iterators) => {
return new Promise((resolve, reject) => {
if (!iterators || iterators.length === 0) {
return resolve([]);
}
let results = [];
for (let i = 0; i < iterators.length; i++) {
const item = iterators[i];
// item 可能不是 Promise 对象，统一转换为 Promise 对象
Promise.resolve(item)
.then((res) => {
results[i] = res; // 按顺序保存对应的结果
// 当所有任务都执行完毕后，resolve一个结果数组
if (results.length === iterators.length) {
resolve(results);
}
})
.catch((e) => {
// 一旦有一个 Promise 失败，立刻 reject
return reject(e);
});
}
});
};
const timeout = (ms) =>
new Promise((resolve, reject) => {
if (!ms) {
reject('未传入时间');
} else {
setTimeout(() => {
resolve(ms);
}, ms);
}
});
promiseAll([timeout(1000), timeout(2000), timeout(), timeout(3000)])
.then((res) => {
console.log(res, 'res');
})
.catch((e) => {
console.log(e, 'e');
});