Node express 4 post submitted an error

  node.js, question

Error missing content-type header status 415

//ajax submission

$.ajax({
 url:'/pics',
 type: 'POST',
 data:'{"upload":true}',
 dataType:'json',
 success:function(data){
 alert('success');
 },
 error:function(err){
 alert(123);
 bracket
 })
 
 Post ('/pics', function () {
 ....
 
 Res.json (//json string});
 })
 
 I have been reminded since the execution.
 unsupported content-Type  status 415

Can you add a content-type?
This sentence indicates that you cannot find the content-type.

response.writeHead(200, { 'Content-Type': 'text/plain' });