Multipart Bodies

Posting data as multipart/form-data

Using FormData API

Browser

const form = new FormData();
form.append('my_field', 'my value');
form.append('my_buffer', new Blob([1,2,3]));
form.append('my_file', fileInput.files[0]);

axios.post('https://example.com', form)

The same result can be achieved using the internal Axios serializer and corresponding shorthand method:

axios.postForm('https://httpbin.org/post', {
  my_field: 'my value',
  my_buffer: new Blob([1,2,3]),
  my_file:  fileInput.files // FileList will be unwrapped as sepate fields
});

HTML form can be passes directly as a request payload

Node.js

import axios from 'axios';

const form = new FormData();
form.append('my_field', 'my value');
form.append('my_buffer', new Blob(['some content']));

axios.post('https://example.com', form)

Since node.js does not currently support creating a Blob from a file, you can use a third-party package for this purpose.

import {fileFromPath} from 'formdata-node/file-from-path'

form.append('my_field', 'my value');
form.append('my_file', await fileFromPath('/foo/bar.jpg'));

axios.post('https://example.com', form)

For Axios older than v1.3.0 you must import form-data package.

const FormData = require('form-data');

const form = new FormData();
form.append('my_field', 'my value');
form.append('my_buffer', new Buffer(10));
form.append('my_file', fs.createReadStream('/foo/bar.jpg'));

axios.post('https://example.com', form)

🆕 Automatic serialization

Starting from v0.27.0, Axios supports automatic object serialization to a FormData object if the request Content-Type header is set to multipart/form-data.

The following request will submit the data in a FormData format (Browser & Node.js):

import axios from 'axios';

axios.post('https://httpbin.org/post', {
  user: {
    name: 'Dmitriy'
  },
  file: fs.createReadStream('/foo/bar.jpg')
}, {
  headers: {
    'Content-Type': 'multipart/form-data'
  }
}).then(({data})=> console.log(data));

Axios FormData serializer supports some special endings to perform the following operations:

• {} - serialize the value with JSON.stringify
• [] - unwrap the array-like object as separate fields with the same key

NOTE: unwrap/expand operation will be used by default on arrays and FileList objects

FormData serializer supports additional options via config.formSerializer: object property to handle rare cases:

• visitor: Function - user-defined visitor function that will be called recursively to serialize the data object to a FormData object by following custom rules.

• dots: boolean = false - use dot notation instead of brackets to serialize arrays and objects;

• metaTokens: boolean = true - add the special ending (e.g user{}: '{"name": "John"}') in the FormData key. The back-end body-parser could potentially use this meta-information to automatically parse the value as JSON.

• indexes: null|false|true = false - controls how indexes will be added to unwrapped keys of flat array-like objects

  • null - don't add brackets (arr: 1, arr: 2, arr: 3)
  • false(default) - add empty brackets (arr[]: 1, arr[]: 2, arr[]: 3)
  • true - add brackets with indexes (arr[0]: 1, arr[1]: 2, arr[2]: 3)

Let's say we have an object like this one:

const obj = {
  x: 1,
  arr: [1, 2, 3],
  arr2: [1, [2], 3],
  users: [{name: 'Peter', surname: 'Griffin'}, {name: 'Thomas', surname: 'Anderson'}],
  'obj2{}': [{x:1}]
};

The following steps will be executed by the Axios serializer internally:

const formData= new FormData();
formData.append('x', '1');
formData.append('arr[]', '1');
formData.append('arr[]', '2');
formData.append('arr[]', '3');
formData.append('arr2[0]', '1');
formData.append('arr2[1][0]', '2');
formData.append('arr2[2]', '3');
formData.append('users[0][name]', 'Peter');
formData.append('users[0][surname]', 'Griffin');
formData.append('users[1][name]', 'Thomas');
formData.append('users[1][surname]', 'Anderson');
formData.append('obj2{}', '[{"x":1}]');

import axios from 'axios';

axios.post('https://httpbin.org/post', {
  'myObj{}': {x: 1, s: "foo"},
  'files[]': document.querySelector('#fileInput').files 
}, {
  headers: {
    'Content-Type': 'multipart/form-data'
  }
}).then(({data})=> console.log(data));

Axios supports the following shortcut methods: postForm, putForm, patchForm which are just the corresponding http methods with the content-type header preset to multipart/form-data.

FileList object can be passed directly:

await axios.postForm('https://httpbin.org/post', document.querySelector('#fileInput').files)

All files will be sent with the same field names: files[];