Error [ERR_HTTP_HEADERS_SENT]: Cannot set headers after they are sent to the client error in node.js project

Question

Here's my code

/*
*
*
*       Complete the API routing below
*
*
*/

'use strict';
const {v4 : uuidv4} = require('uuid')
function Update(n){
  let filter={$set:{}};
  console.log("update"+JSON.stringify(n))
if(n.issue_title!=""){filter.$set.issue_title=n.issue_title}
if(n.issue_text!=""){filter.$set.issue_text=n.issue_text}
if(n.created_by!=""){filter.$set.created_by=n.created_by}
filter.$set.updated_on=new Date;
if(n.assigned_to!=""){filter.$set.assigned_to=n.assigned_to}
if(n.status_text!=""){filter.$set.status_text=n.status_text}
if(n.open==="false"){filter.$set.open=false}
console.log("filter"+JSON.stringify(filter))
return filter;
}
const checkResult = (want, reference) => {
  // creating a new temp objecct OUTSIDE of the for loop
  let temp = {}
  
  // Array of the reference keys
  const keys = Object.keys(reference)

  // looping over keys in reference
  for (let i = 0; i < keys.length; i++) {
  
    // The current key
    const key = keys[i]
    
    // if the key is included in the 'want' list
    if (key in want) {

      // set a property in the temp object, but with a different value
      temp[key] = 1
    }
  }

  // when we are done, return the object
  console.log(JSON.stringify(temp))
  return temp
}
const Datas = require('../Models/datas');
module.exports = function (app) {

  app.route('/api/issues/:project')
  
    .get(function (req, res){
      console.log(JSON.stringify(req.query))
        if(Object.keys(req.query).length === 0){Datas.find().then((data,err)=>{
           console.log("correct")
          res.json(data)
        })}
        else {
          let find={
             "issue_title": 0,
             "issue_text": 0,
             "created_on":0,
             "updated_on":0,
             "created_by":0,
             "assigned_to":0,
             "open":0,
             "status_text":0,
             "__v":0
          }
          let afterFind=checkResult(find,req.query)
          console.log("got here"+afterFind)
          Datas.find(req.query).select(afterFind).exec()
          .then((data,err)=>{
               if(err){
                 res.send(err)
               }
               res.json(data)
            }
          )
        }
    })
    
    .post(function (req, res){
      let main=req.body;
      console.log(main)
      if(req.body.issue_title==""||req.body.issue_text==""||req.body.created_by==""){
       res.json({ error: 'required field(s) missing' })
      }
   else {
     const id1 = uuidv4()
      let savedata=new Datas({
        "_id":id1,
        "issue_title":req.body.issue_title,
        "issue_text":req.body.issue_text,
        "created_on":new Date(),
        "updated_on":new Date(),
        "created_by":req.body.created_by,
        "assigned_to":req.body.assigned_to,
        "open":true,
        "status_text":req.body.status_text
      })
      savedata.save((err,data)=>{
        if(err){res.json({error:"error has been occurred"})}
        else {
        res.json({
        "_id":id1,
        "issue_title":req.body.issue_title,
        "issue_text":req.body.issue_text,
        "created_on":new Date(),
        "updated_on":new Date(),
        "created_by":req.body.created_by,
        "assigned_to":req.body.assigned_to,
        "open":true,
        "status_text":req.body.status_text
      })};
      })
    }
    })
    
    .put( function (req, res){
    console.log(req.body)
    let obj=req.body

    if(!obj.hasOwnProperty(_id)){
       res.json({ error: 'missing _id' })
    }
    else if(obj.issue_title==""||obj.issue_text==""||obj.created_by==""||obj.assigned_to==""||obj.status_text==""){
      res.json({ error: 'no update field(s) sent', '_id': obj._id })
    }
      Datas.findOneAndUpdate({"_id":req.body._id}, Update(req.body),{new:true}).then((data,err)=>{
        if(err){res.json({ error: 'could not update', '_id': obj._id })}
        console.log(data)
         res.json( { result: 'successfully updated', '_id': data._id })
         })
    })
    
    .delete(function (req, res){
  console.log(req.body)
  let obj=req.body
     if(!obj.hasOwnProperty("_id")){
       res.json({ error: 'missing _id' })
    }
  Datas.findByIdAndRemove(req.body,(err,data)=>{
    if(err){res.json({ error: 'could not delete', '_id': obj._id })}
    res.json({ result: 'successfully deleted', '_id': obj._id })
  })
    });
    
};

does anyone know what is the error

/home/runner/boilerplate-project-issuetracker/node_modules/mongoose/lib/helpers/promiseOrCallback.js:19 throw error; ^

Error [ERR_HTTP_HEADERS_SENT]: Cannot set headers after they are sent to the client at ServerResponse.setHeader (_http_outgoing.js:518:11) at ServerResponse.header (/home/runner/boilerplate-project-issuetracker/node_modules/express/lib/response.js:771:10) at ServerResponse.send (/home/runner/boilerplate-project-issuetracker/node_modules/express/lib/response.js:170:12) at ServerResponse.json (/home/runner/boilerplate-project-issuetracker/node_modules/express/lib/response.js:267:15) at /home/runner/boilerplate-project-issuetracker/routes/api.js:146:17 at /home/runner/boilerplate-project-issuetracker/node_modules/mongoose/lib/model.js:4850:16 at /home/runner/boilerplate-project-issuetracker/node_modules/mongoose/lib/model.js:4850:16 at /home/runner/boilerplate-project-issuetracker/node_modules/mongoose/lib/helpers/promiseOrCallback.js:16:11 at /home/runner/boilerplate-project-issuetracker/node_modules/mongoose/lib/model.js:4873:21 at /home/runner/boilerplate-project-issuetracker/node_modules/mongoose/lib/query.js:4389:18 at model.Query.Query._findAndModify (/home/runner/boilerplate-project-issuetracker/node_modules/mongoose/lib/query.js:3460:12) at model.Query. (/home/runner/boilerplate-project-issuetracker/node_modules/mongoose/lib/query.js:3421:8) at model.Query._wrappedThunk [as _findOneAndRemove] (/home/runner/boilerplate-project-issuetracker/node_modules/mongoose/lib/helpers/query/wrapThunk.js:16:8) at /home/runner/boilerplate-project-issuetracker/node_modules/kareem/index.js:370:33 at processTicksAndRejections (internal/process/task_queues.js:79:11) Emitted 'error' event on Function instance at: at /home/runner/boilerplate-project-issuetracker/node_modules/mongoose/lib/model.js:4852:13 at /home/runner/boilerplate-project-issuetracker/node_modules/mongoose/lib/helpers/promiseOrCallback.js:16:11 [... lines matching original stack trace ...] at processTicksAndRejections (internal/process/task_queues.js:79:11) { code: 'ERR_HTTP_HEADERS_SENT' } npm ERR! code ELIFECYCLE npm ERR! errno 1 npm ERR! [email protected] start: node server.js npm ERR! Exit status 1 npm ERR! npm ERR! Failed at the [email protected] start 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! /home/runner/.np

Actually above code section is the only thing i edited and all other section are perfectly fine,all debugged perfectly

And I suppose you should add return after res.json calls. — Anatoly

Bipin Shrestha Bipin Shrestha · Accepted Answer · 2020-12-22T05:47:59

 let afterFind = checkResult(find, req.query);
    console.log('got here' + afterFind);
    models.Users.find(req.query)
      .select(afterFind)
      .exec()
      .then((data, err) => {
        if (err) {
          res.send(err); // YOU NEED TO RETURN HERE AS return res.send(err)
        }
        res.json(data);
      });

You need to return the response so that it doesn't reach to the next response. You have a couple of other places where you need to return the response.

If you don't know where to keep return exactly. It's better to keep return in every res.send/res.json

Error [ERR_HTTP_HEADERS_SENT]: Cannot set headers after they are sent to the client error in node.js project

1 Answers