我试图创建一个脚本，使用node js从多个URL下载页面，但是循环不想等待请求完成并继续打印，我还得到了一个使用async for循环的提示，但是它仍然没有工作。
这是我的代码
function GetPage(url){
console.log(` Downloading page ${url}`);
request({
url: `${url}`
},(err,res,body) => {
if(err) throw err;
console.log(` Writing html to file` );
fs.writeFile(`${url}.html`,`${body}`,(err) => {
if(err) throw err;
console.log('saved');
});
});
}
var list = [ 'https://www.someurl.com/page1.html', 'https://www.someurl.com/page2.html', 'https://www.someurl.com/page3.html' ]
const main = async () => {
for(let i = 0; i < list.length; i++){
console.log(` processing ${list[i]}`);
await GetPage(list[i]);
}
};
main().catch(console.error);
输出:
processing https://www.someurl.com/page1.html
Downloading page https://www.someurl.com/page1.html
processing https://www.someurl.com/page2.html
Downloading page https://www.someurl.com/page2.html
processing https://www.someurl.com/page3.html
Downloading page https://www.someurl.com/page3.html
Writing html to file
Writing html to file
saved
saved
Writing html to file
saved
因为循环不等待回调完成，它将继续执行回调。您需要将getPage函数转换为promise或使用promise.all，如下所示。
var list = [
"https://www.someurl.com/page1.html",
"https://www.someurl.com/page2.html",
"https://www.someurl.com/page3.html",
];
function getPage(url) {
return new Promise((resolve, reject) => {
console.log(` Downloading page ${url}`);
request({ url: `${url}` }, (err, res, body) => {
if (err) reject(err);
console.log(` Writing html to file`);
fs.writeFile(`${url}.html`, `${body}`, (writeErr) => {
if (writeErr) reject(writeErr);
console.log("saved");
resolve();
});
});
});
}
const main = async () => {
return new Promise((resolve, reject) => {
let promises = [];
list.map((path) => promises.push(getPage(path)));
Promise.all(promises).then(resolve).catch(reject);
});
};
main().catch(console.error);
