x-www-form-urlencoded format

URLSearchParams

By default, axios serializes JavaScript objects to JSON. To send data in the application/x-www-form-urlencoded format instead, you can use the URLSearchParams API, which is supported in the vast majority of browsers, and Node starting with v10 (released in 2018).

const params = new URLSearchParams({ foo: 'bar' });
params.append('extraparam', 'value');
axios.post('/foo', params);

Query string <Badge type="danger" text="Very old" />

For older browsers or environments without URLSearchParams, you can use the qs library to serialize objects to the application/x-www-form-urlencoded format.

const qs = require('qs');
axios.post('/foo', qs.stringify({ bar: 123 }));

For full control over headers and method, pass qs.stringify output as the request data and set Content-Type explicitly:

import qs from 'qs';

const data = { bar: 123 };
const options = {
  method: 'POST',
  headers: { 'content-type': 'application/x-www-form-urlencoded' },
  data: qs.stringify(data),
  url: '/foo',
};
axios(options);

In very old versions of Node.js, you can use the built-in querystring module that ships with Node.js. Note that this module has been deprecated in Node.js v16 — prefer URLSearchParams or qs for new code.

const querystring = require('querystring');
axios.post('https://something.com/', querystring.stringify({ foo: 'bar' }));

::: tip Prefer qs for nested objects The qs library is preferable if you need to stringify nested objects, as the querystring method has known issues with that use case. :::

Automatic serialization to URLSearchParams <Badge type="tip" text="New" />

Starting from v0.21.0, axios automatically serializes JavaScript objects to URLSearchParams if the Content-Type header is set to application/x-www-form-urlencoded. This means that you can pass a JavaScript object directly to the data property of the axios request config. For example when passing data to a POST request:

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

await axios.postForm('https://postman-echo.com/post', data, {
  headers: { 'content-type': 'application/x-www-form-urlencoded' },
});

The data object will be automatically serialized to URLSearchParams and sent in the application/x-www-form-urlencoded format. The server will receive the following data:

{
  "x": "1",
  "arr[]": ["1", "2", "3"],
  "arr2[0]": "1",
  "arr2[1][0]": "2",
  "arr2[2]": "3",
  "users[0][name]": "Peter",
  "users[0][surname]": "Griffin",
  "users[1][name]": "Thomas",
  "users[1][surname]": "Anderson"
}

If your backend body-parser (like body-parser of express.js) supports nested objects decoding, you will get the same object on the server-side automatically

Depth limit for params serialization

When axios serializes a params object via AxiosURLSearchParams, the same recursive walker used by the FormData serializer is called. A maxDepth option (default 100) limits how deeply it will recurse. Payloads exceeding the limit throw an AxiosError with code: 'ERR_FORM_DATA_DEPTH_EXCEEDED' instead of overflowing the call stack.

// Raise the limit if your params object legitimately nests deeper than 100 levels:
axios.get('/api', { params: deepObject, paramsSerializer: { maxDepth: 200 } });

::: warning Security note Only raise maxDepth if your schema genuinely requires it. The default of 100 protects server-side code that forwards client-controlled data to axios as params from DoS attacks via deeply nested objects. :::

var app = express();

app.use(bodyParser.urlencoded({ extended: true })); // support encoded bodies

app.post('/', function (req, res, next) {
  // echo body as JSON
  res.send(JSON.stringify(req.body));
});

server = app.listen(3000);