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 Very old

For older browsers, you can use the querystring library to serialize objects to the application/x-www-form-urlencoded format.

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

In very old versions of Node.js, you can use the querystring module that comes with Node.js.

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

Automatic serialization to URLSearchParams 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",
  "arr3[]": ["1", "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

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);