目标
通过concurRequest(urls, maxNums)
的形式发起并发请求,参数为url数组和最大并发数量,返回值为Promise,成功结果为原url顺序的响应结果数组。
代码实现
concurRequest.js
/**
* 并发请求
* @param {string[]} urls 待请求的 url 数组
* @param {number} maxNum 最大并发数
*/
function concurRequest(urls, maxNum) {
return new Promise((resolve) => {
if (urls.length === 0) {
resolve([]);
return;
}
const results = [];
let index = 0; // 下一个请求的下标
let count = 0; // 当前请求完成的数量
// 发送请求
async function request() {
if (index === urls.length) {
return;
}
const i = index;
const url = urls[index];
index++;
try {
const resp = await fetch(url);
// resp加入到 results
results[i] = resp;
} catch (err) {
// err加入到 results
results[i] = err;
} finally {
// 判断是否所有的请求都已完成
count++;
if (count === urls.length) {
// 所有请求完成,返回结果
resolve(results);
}
request();
}
}
const times = Math.min(maxNum, urls.length);
for (let i = 0; i < times; i++) {
request();
}
});
}
test.html
<!DOCTYPE html>
<html lang="en">
<head>
<meta charset="UTF-8">
<meta name="viewport" content="width=device-width, initial-scale=1.0">
<title>并发请求</title>
</head>
<body>
<script src="./concurRequest.js"></script>
<script>
const urls = [];
for(let i = 1; i <= 20; i++){
urls.push(`https://jsonplaceholder.typicode.com/todos/${i}`);
}
concurRequest(urls, 3).then((resps) => {
console.log(resps);
})
</script>
</body>
</html>
可通过浏览器调试工具查看测试结果及请求过程。
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