如何使用 async/await 实现 Promise.all 的效果
更多描述 如获取三个用户的信息，使用
Promise.all的写法
const users = await Promise.all(getUser(1), getUser(2), getUser(3));那如何不使用 Promise.all 实现以上效果
Issue 欢迎在 Gtihub Issue 中回答此问题: Issue 242
Author 回答者: shfshanyue
使用 async/await 实现
const user1 = getUser(1);
const user2 = getUser(2);
const user3 = getUser(3);
const u1 = await user1;
const u2 = await user2;
const u3 = await user3;Author 回答者: Misxiao
const all = (list) => {
const res = new Promise((resolve, reject) => {
let length = list && list.length
let count = 0
let result = []
if(!list || list.length === 0) {
resolve(result)
}
list.forEach(async (item, index) => {
try {
const res = await item
result[index] = res
count ++
if(count === length) {
resolve(result)
}
} catch(err) {
reject(err)
}
});
})
return res
}使用
async/await实现const user1 = getUser(1); const user2 = getUser(2); const user3 = getUser(3); const u1 = await user1; const u2 = await user2; const u3 = await user3;
这个和上面的 Promise.all 并不一样吧。Promise.all 是并行操作，await 这个是串行操作
如获取三个用户的信息，使用
Promise.all的写法const users = await Promise.all(getUser(1), getUser(2), getUser(3));那如何不使用
Promise.all实现以上效果
Promise.all 后面的参数为数组。。。
let req1 = () =>
fetch(
`https://github.com/shfshanyue/Daily-Question/issues?page=1&q=is%3Aissue+is%3Aopen`,
);
let req2 = () =>
fetch(
`https://github.com/shfshanyue/Daily-Question/issues?page=2&q=is%3Aissue+is%3Aopen`,
);
let req3 = () =>
fetch(
`https://github.com/shfshanyue/Daily-Question/issues?page=3&q=is%3Aissue+is%3Aopen`,
);
// promise.all
const res = await Promise.all([req1(), req2(), req3()]);
const res1 = req1();
const res2 = req2();
const res3 = req3();
// await
const u1 = await res1;
const u2 = await res2;
const u3 = await res3;
所以这个题的答案是
tan90° 不存在
Author 回答者: jeff-wangzhen
看了一篇这个，好像可以 https://blog.csdn.net/github_38589282/article/details/79268484
Author 回答者: iamphc
如有错误，欢迎指正
async function foo(promise) {
const t = [];
for (let p of promise) {
// 检查传参
if (p instanceof Promise === false) {
throw new Error("传参错误");
}
// 并行触发
(async () => {
try {
const r = await p;
t.push(r);
} catch (err) {
// 捕获异常
return err;
}
})();
}
// 轮询
const res = await new Promise((resolve) => {
const timer = setInterval(() => {
if (t.length === promise.length) {
clearInterval(timer);
resolve(t);
}
}, 1000);
});
return res;
}Author 回答者: justorez
所以这个题的答案是
tan90° 不存在
@ghost
<script>
async function fn() {
const req = (i) =>
fetch(
`https://github.com/shfshanyue/Daily-Question/issues?page=${i}&q=is%3Aissue+is%3Aopen`,
{
mode: "no-cors",
},
);
// promise.all
const res = await Promise.all([req(1), req(2), req(3)]);
// await
const res1 = req(4);
const res2 = req(5);
const res3 = req(6);
const u1 = await res1;
const u2 = await res2;
const u3 = await res3;
}
fn();
</script>