How to resolve setHeader issue in nodejs - node.js

Question

I have done file uploading process in my application using connect-multiparty.I can upload file and move to local folder.Everything is working perfect except below issue.I do not know why i am getting this error.How to resolve this issue?How to avoid this error.
app.js:
var multipart = require('connect-multiparty');
var multipartMiddleware = multipart();
var fs = require('fs');
app.post('/api/upload', multipartMiddleware, (req, res) => {
res.json({ 'message': req.files });
var tmp_path = req.files.uploads[0].path;
var target_path = './uploads/' + req.files.uploads[0].name;
fs.rename(tmp_path, target_path, function(err) {
if (err) throw err;
console.log("Upload started")
fs.unlink(tmp_path, function() {
if (err) throw err;
res.send('File uploaded to: ' + target_path);
});
});
res.end();
});
upload.component.ts:
upload(){
let formData = new FormData();
for(var i = 0; i < this.uploadedFiles.length; i++) {
formData.append("uploads[]", this.uploadedFiles[i], this.uploadedFiles[i].name);
}
this.http.post(environment.apiBaseUrl+'/upload', formData)
.subscribe((response)=>{
console.log('response receved is ', response);
})
}
Error:
_http_outgoing.js:526
throw new ERR_HTTP_HEADERS_SENT('set');
^
Error [ERR_HTTP_HEADERS_SENT]: Cannot set headers after they are sent to the client
at ServerResponse.setHeader (_http_outgoing.js:526:11)
at ServerResponse.header (C:\xampp\htdocs\testing\server\node_modules\express\lib\response.js:767:10)
at ServerResponse.send (C:\xampp\htdocs\testing\server\node_modules\express\lib\response.js:170:12)
at C:\xampp\htdocs\testing\server\app.js:65:17
at FSReqCallback.oncomplete (fs.js:154:23) {
code: 'ERR_HTTP_HEADERS_SENT'
}
npm ERR! code ELIFECYCLE
npm ERR! errno 1
npm ERR! project#1.0.0 dev: `node app.js`
npm ERR! Exit status 1
npm ERR!
npm ERR! Failed at the project#1.0.0 dev script.
npm ERR! This is probably not a problem with npm. There is likely additional logging output above.
npm ERR! A complete log of this run can be found in:
npm ERR! C:\Users\ADMIN\AppData\Roaming\npm-cache\_logs\2020-05-21T17_06_06_701Z-debug.log