Nodejs通过jquery / ajax表示发布查询，在读取响应时无法设置头文件错误(Nodejs express posting query via jquery/ajax can't

Nodejs通过jquery / ajax表示发布查询，在读取响应时无法设置头文件错误(Nodejs express posting query via jquery/ajax can't set headers error while reading response)

我试图通过jQuery和Ajax发布查询后从我的服务器读取响应。我认为这是因为我试图使用res.render呈现页面并在使用res.end从我的数据库接收数据后写出响应。但我不知道如何解决它，因为我是NodeJS express的新手。

这是我的nodejs部分，它接收请求，查询数据库并尝试发送响应：

app.all('/Search', function(req, res) { res.render('search'); var query = req.body.username; if (req.body.username) { db.collection('users').find({username: query}).toArray(function(err, result) { if (err) return console.log(err); console.log("Request body = "+req.body.username); console.log(result); res.writeHead(200, { 'Content-Type': 'application/json' }); res.end(JSON.stringify(data)); }); } });

这是search.ejs html页面，其中嵌入了jquery：

<!DOCTYPE html> <html lang="en"> <script src="https://ajax.googleapis.com/ajax/libs/jquery/3.2.1/jquery.min.js"></script> <head> <meta charset="UTF-8"> <title>MY APP</title> </head> <body> <div style="margin: 0 auto;width: 500px;"> <form id="searchForm" action="/Search" method="post" style="margin: 0 auto; width: 200px; margin-top: 100px;"> <input id="username" type="text" placeholder="Search" name="username" style="margin: 20px auto; font-size: 50px;">  <button type="submit" style="margin: 20px auto; font-size: 50px;">Submit</button> </form> </div> <script type="text/javascript"> $('#searchForm').on('submit', function (event) { console.log("HI"); event.preventDefault(); // Stop the form from causing a page refresh. var data = { username: $('#username').val() }; console.log("DATA === "+data); $.ajax({ url: 'http://localhost:3000/Search', data: data, method: 'POST' }).then(function (response) { console.log("Response ="+response); // Do stuff with the response, like add it to the page dynamically. $('body').append(response); }).catch(function (err) { console.error(err); }); }); </script> </body> </html>

这是终端的输出：

Server started at port:3000 Request body = abc [ { _id: 5938c2f9453e40053965e9ec, username: 'abc', specialty: 'dsfsaddfjk', address: 'oidjfioa' } ] /home/vineet/Desktop/serene-brushlands-55292/node_modules/mongodb/lib/utils.js:123 process.nextTick(function() { throw err; }); ^

错误：发送后无法设置标头。

at ServerResponse.setHeader (_http_outgoing.js:371:11) at ServerResponse.writeHead (_http_server.js:183:21) at /home/vineet/Desktop/serene-brushlands-55292/app.js:52:10 at handleCallback (/home/vineet/Desktop/serene-brushlands-55292/node_modules/mongodb/lib/utils.js:120:56) at /home/vineet/Desktop/serene-brushlands-55292/node_modules/mongodb/lib/cursor.js:860:16 at handleCallback (/home/vineet/Desktop/serene-brushlands-55292/node_modules/mongodb-core/lib/cursor.js:171:5) at setCursorDeadAndNotified (/home/vineet/Desktop/serene-brushlands-55292/node_modules/mongodb-core/lib/cursor.js:505:3) at nextFunction (/home/vineet/Desktop/serene-brushlands-55292/node_modules/mongodb-core/lib/cursor.js:651:7) at Cursor.next [as _next] (/home/vineet/Desktop/serene-brushlands-55292/node_modules/mongodb-core/lib/cursor.js:692:3) at fetchDocs (/home/vineet/Desktop/serene-brushlands-55292/node_modules/mongodb/lib/cursor.js:856:10) at /home/vineet/Desktop/serene-brushlands-55292/node_modules/mongodb/lib/cursor.js:879:7 at handleCallback (/home/vineet/Desktop/serene-brushlands-55292/node_modules/mongodb-core/lib/cursor.js:171:5) at nextFunction (/home/vineet/Desktop/serene-brushlands-55292/node_modules/mongodb-core/lib/cursor.js:682:5) at /home/vineet/Desktop/serene-brushlands-55292/node_modules/mongodb-core/lib/cursor.js:593:7 at queryCallback (/home/vineet/Desktop/serene-brushlands-55292/node_modules/mongodb-core/lib/cursor.js:232:18) at /home/vineet/Desktop/serene-brushlands-55292/node_modules/mongodb-core/lib/connection/pool.js:469:18

我在jQuery存根中收到的响应是search.ejs本身的html。请帮忙！！

I am trying to read responses from my server after posting a query via jQuery and Ajax. I think it's because I am trying to render the page using res.render and writing out a response after receiving data from my db using res.end. But I don't know how to resolve it as I am a newbie to NodeJS express.

Here is my nodejs part that receives the request, queries the db and tries to send the response:

app.all('/Search', function(req, res) { res.render('search'); var query = req.body.username; if (req.body.username) { db.collection('users').find({username: query}).toArray(function(err, result) { if (err) return console.log(err); console.log("Request body = "+req.body.username); console.log(result); res.writeHead(200, { 'Content-Type': 'application/json' }); res.end(JSON.stringify(data)); }); } });

Here is the search.ejs html page with the jquery embedded in it:

<!DOCTYPE html> <html lang="en"> <script src="https://ajax.googleapis.com/ajax/libs/jquery/3.2.1/jquery.min.js"></script> <head> <meta charset="UTF-8"> <title>MY APP</title> </head> <body> <div style="margin: 0 auto;width: 500px;"> <form id="searchForm" action="/Search" method="post" style="margin: 0 auto; width: 200px; margin-top: 100px;"> <input id="username" type="text" placeholder="Search" name="username" style="margin: 20px auto; font-size: 50px;">  <button type="submit" style="margin: 20px auto; font-size: 50px;">Submit</button> </form> </div> <script type="text/javascript"> $('#searchForm').on('submit', function (event) { console.log("HI"); event.preventDefault(); // Stop the form from causing a page refresh. var data = { username: $('#username').val() }; console.log("DATA === "+data); $.ajax({ url: 'http://localhost:3000/Search', data: data, method: 'POST' }).then(function (response) { console.log("Response ="+response); // Do stuff with the response, like add it to the page dynamically. $('body').append(response); }).catch(function (err) { console.error(err); }); }); </script> </body> </html>

And here is the output in the terminal:

Server started at port:3000 Request body = abc [ { _id: 5938c2f9453e40053965e9ec, username: 'abc', specialty: 'dsfsaddfjk', address: 'oidjfioa' } ] /home/vineet/Desktop/serene-brushlands-55292/node_modules/mongodb/lib/utils.js:123 process.nextTick(function() { throw err; }); ^

Error: Can't set headers after they are sent.

at ServerResponse.setHeader (_http_outgoing.js:371:11) at ServerResponse.writeHead (_http_server.js:183:21) at /home/vineet/Desktop/serene-brushlands-55292/app.js:52:10 at handleCallback (/home/vineet/Desktop/serene-brushlands-55292/node_modules/mongodb/lib/utils.js:120:56) at /home/vineet/Desktop/serene-brushlands-55292/node_modules/mongodb/lib/cursor.js:860:16 at handleCallback (/home/vineet/Desktop/serene-brushlands-55292/node_modules/mongodb-core/lib/cursor.js:171:5) at setCursorDeadAndNotified (/home/vineet/Desktop/serene-brushlands-55292/node_modules/mongodb-core/lib/cursor.js:505:3) at nextFunction (/home/vineet/Desktop/serene-brushlands-55292/node_modules/mongodb-core/lib/cursor.js:651:7) at Cursor.next [as _next] (/home/vineet/Desktop/serene-brushlands-55292/node_modules/mongodb-core/lib/cursor.js:692:3) at fetchDocs (/home/vineet/Desktop/serene-brushlands-55292/node_modules/mongodb/lib/cursor.js:856:10) at /home/vineet/Desktop/serene-brushlands-55292/node_modules/mongodb/lib/cursor.js:879:7 at handleCallback (/home/vineet/Desktop/serene-brushlands-55292/node_modules/mongodb-core/lib/cursor.js:171:5) at nextFunction (/home/vineet/Desktop/serene-brushlands-55292/node_modules/mongodb-core/lib/cursor.js:682:5) at /home/vineet/Desktop/serene-brushlands-55292/node_modules/mongodb-core/lib/cursor.js:593:7 at queryCallback (/home/vineet/Desktop/serene-brushlands-55292/node_modules/mongodb-core/lib/cursor.js:232:18) at /home/vineet/Desktop/serene-brushlands-55292/node_modules/mongodb-core/lib/connection/pool.js:469:18

The response that I receive in the jQuery stub is the html for search.ejs itself. Please help!!