GraphQL File Uploading (Without Apollo…)

February 10, 2020

Loading Timber at Southampton Docks – C. R. W. Nevinson

Update January 6, 2021: I realized the multi-file upload example had some errors in it. They’re fixed now, and everything should be working as expected.


This quick tutorial explains how to upload files with GraphQL using only plain JavaScript and no frameworks or libraries. It’s not meant as a complete tutorial as I won’t be covering the backend side of the implementation.

The specs

A general specification for file uploads through GraphQL can be found on Github.

The idea is to send a multi-part form request to the server which enables you to easily upload multiple files in one request.

As the specs point out, the following GraphQL query should be sent to the server:

{
  query: `
    mutation($file: Upload!) {
      singleUpload(file: $file) {
        id
      }
    }
  `,
  variables: {
    file: File
  }
}

Which then will be uploaded as a multi-part form request:

--------------------------cec8e8123c05ba25
Content-Disposition: form-data; name="operations"

{ "query": "mutation ($file: Upload!) { singleUpload(file: $file) { id } }", "variables": { "file": null } }
--------------------------cec8e8123c05ba25
Content-Disposition: form-data; name="map"

{ "0": ["variables.file"] }
--------------------------cec8e8123c05ba25
Content-Disposition: form-data; name="0"; filename="a.txt"
Content-Type: text/plain

Alpha file content.

--------------------------cec8e8123c05ba25--

The details

Let’s have a look at the different parts of the form request.

  1. operations contains the GraphQL query:
--------------------------cec8e8123c05ba25
Content-Disposition: form-data; name="operations"
{ "query": "mutation ($file: Upload!) { singleUpload(file: $file) { id } }", "variables": { "file": null } }
  1. map is responsible for the mapping between the file-variable in the GraphQL query and the file attached to the request:
--------------------------cec8e8123c05ba25
Content-Disposition: form-data; name="map"

{ "0": ["variables.file"] }
  1. And the file fields contain the actual files themselves:
--------------------------cec8e8123c05ba25
Content-Disposition: form-data; name="0"; filename="a.txt"
Content-Type: text/plain

Alpha file content.

--------------------------cec8e8123c05ba25--

So far so good. But how do we implement a request like this in plain JavaScript?

The client

Let’s imagine we have the following HTML markup for a form:

<form action="/graphql">
  <input type="file" name="myfile" />
  <button>Upload</button>
</form>

All we need to do is create a formData request like so:

const formData = new FormData()

Create the operations field, containing the GraphQL query, and append it to the form request:

const operations = `{ "query": "mutation ($file: Upload!) { singleUpload(file: $file) { id } }", "variables": { "file": null } }`
formData.append("operations", operations)

Add the map field with the variables and the actual file:

const map = `{"0": ["variables.file"]}`
formData.append("map", map)
formData.append("0", event.target.files[0])

For the sake of this example I referenced the file directly from the form, assuming the upload is triggered by an event.

And lastly, send it to the server, using fetch():

fetch("/graphql", {
  body: formData,
  method: "post",
})

If all goes well and your server is implemented according to the previously mentioned specification, you should be able to upload files with just plain old JavaScript. No need for a fancy library or framework. Which doesn’t mean that those frameworks are bad by the way… I just feel sometimes it’s not needed.

Multiple files

In case you want to upload multiple files, all we have to do is modify the GraphQL query to contain a list of files instead of just one file:

{
  query: `
    mutation($file: [Upload!]!) {
      multipleUpload(files: $files) {
        id
      }
    }
  `,
  variables: {
    files: [
      File,
      File
    ]
  }
}

Define the operations part:

const operations = `{ "query": "mutation ($files: [Upload!]!) { multipleUpload(files: $files) { id } }", "variables": { "files": [null, null] } }`
formData.append("operations", operations)

Add the mappings between the files and the variables to the map operation and append the files:

const map = `{"0": ["variables.files.0"], "1": ["variables.files.1"]}`
formData.append("map", map)
formData.append("0", event.target.files[0])
formData.append("1", event.target.files[1])

The rest is the same as the one-file example.

If you have questions, concerns or just want to say hi 👋, hit me up on Twitter.

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