How do I upload a file with fetch method in react?

Question

I am working on a react component where I want to upload a excel file to a server. Here is what I am trying. But it gives me an empty object when I console request body

<input type="file" id="avatar" name="avatar" onChange={this.fileHandler.bind(this)} style={{"padding":"10px"}}/>

Here is file handler method which will execute when input file changed:

fileHandler = (event) => {
        event.preventDefault();
        let fileObj = event.target.files[0];
        console.log(fileObj);
        //console.log(JSON.stringify(fileObj));

        var data = new FormData()
        data.append('file', fileObj)

        fetch("/upload", {
            method: 'POST',
            body: data
        }).then(function(response) {
            if (response.status >= 400) {
                throw new Error("Bad response from server");
            }
            return response.text();
        }).then(function(data) {
            console.log(data)
        }).catch(function(err) {
            console.log(err)
        });
}

Here is the server code to upload a file.

app.post('/upload', function(req, res) {
        console.log(req.body); // Output : {} or undefined
        /*try {
            if(!req.files) {
                res.send({
                    status: false,
                    message: 'No file uploaded'
                });

            } else {
                let avatar = req.files.avatar;

                //Use the mv() method to place the file in upload directory (i.e. "uploads")
                avatar.mv('./uploads/' + avatar.name);

                //send response
                res.send({
                    status: true,
                    message: 'File is uploaded',
                    data: {
                        name: avatar.name,
                        mimetype: avatar.mimetype,
                        size: avatar.size
                    }
                });
            }
        } catch (err) {
            res.status(500).send(err);
        }*/
     })

If I try below using form action it is giving me correct output in req.files but I don't want to redirect.

<form id="myForm" method="post" encType="multipart/form-data" action="/upload">
  <input type="hidden" name="msgtype" value="2"/>
  <input type="file" id="avatar" name="avatar" onChange={this.fileHandler.bind(this)} style={{"padding":"10px"}}/>
  <input type="submit" value="Upload" />
</form>

Also I don't want to use axios as I am using the same fetch request for all other execution. Any help is appreciated.

I got this 1st result by doing so and it has everything well explained in it flaviocopes.com/how-to-upload-files-fetch — Zohaib Ijaz
– Zohaib Ijaz, Commented Apr 9, 2020 at 12:15
@ZohaibIjaz I am working on this since long time and I tried everything as per suggestion but no luck. — Vaibhav Gidde
– Vaibhav Gidde, Commented Apr 9, 2020 at 12:21
@ZohaibIjaz yes, the same I did as you can compare the code with the link you have posted but output is undefined — Vaibhav Gidde
– Vaibhav Gidde, Commented Apr 9, 2020 at 12:27

Vaibhav Gidde · Accepted Answer · 2020-04-28 04:56:08Z

Finally, I am able to deal with the correct request parameters using fetch. Here is the solution which I tried and working as expected:

<form id="myForm" method="post" encType="multipart/form-data" action="/upload" onSubmit={this.fileSubmit.bind(this)}>
  <input type="hidden" name="msgtype" value="2"/>
  <input type="file" id="avatar" name="avatar" onChange={this.fileHandler.bind(this)} style={{"padding":"10px"}}/>
  <input type="submit" value="Upload" />
</form>

and here is the submit handler:

fileSubmit = (event) => {
  event.preventDefault();
  fetch(event.target.action, {
      method: 'POST',
      body: new FormData(event.target) // event.target is the form

  }).then((resp) => {
      return resp.json();
      //console.log(resp.json());

  }).then((body) => {
      // TODO handle body
      console.log(body);
      if(body.status) {
          alert(body.message);
      }
      else {
          alert("Please Select a file to upload");
      }
  }).catch((error) => {
      // TODO handle error
      //
  });

and on server side I am able to get req.files as well as the req.body.

app.post('/upload', function(req, res) {
        console.log(req.body); // which gives me form data
        console.log(req.files); // which gives me file object
});

Vaibhav Gidde · Accepted Answer · 2020-04-23 10:19:55Z

I really don't know what I am doing wrong with fetch but I achieved file upload by redirecting form's action to an invisible . Here I am able to prevent form redirect.

<iframe name="dummyframe" id="dummyframe" style={{"display": "none"}}></iframe>
<form id="myForm" method="post" encType="multipart/form-data" action="/upload" target="dummyframe">
  <input type="hidden" name="msgtype" value="2"/>
  <input type="file" id="avatar" name="avatar" onChange={this.fileHandler.bind(this)} style={{"padding":"10px"}}/>
  <input type="submit" value="Upload" />
</form>

So without fetch I am getting the file object at my server side like below:

app.post('/upload', function(req, res) {
        console.log(req.files); // Output : {avatar:{name:"", data: "", size:"", mimetype:""}}
})

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