How do I POST a x-www-form-urlencoded request using Fetch?

Even simpler:

fetch('https://example.com/login', {
    method: 'POST',
    body: new URLSearchParams({
        'userName': '[email protected]',
        'password': 'Password!',
        'grant_type': 'password'
    })
});

Docs: https://developer.mozilla.org/en-US/docs/Web/API/WindowOrWorkerGlobalScope/fetch

Use URLSearchParams

https://developer.mozilla.org/en-US/docs/Web/API/URLSearchParams

var data = new URLSearchParams();
data.append('userName', '[email protected]');
data.append('password', 'Password');
data.append('grant_type', 'password');

Just did this and UrlSearchParams did the trick Here is my code if it helps someone

import 'url-search-params-polyfill';
const userLogsInOptions = (username, password) => {



// const formData = new FormData();
  const formData = new URLSearchParams();
  formData.append('grant_type', 'password');
  formData.append('client_id', 'XXXX-app');
  formData.append('username', username);
  formData.append('password', password);
  return (
    {
      method: 'POST',
      headers: {
        // "Content-Type": "application/json; charset=utf-8",
        "Content-Type": "application/x-www-form-urlencoded",
    },
      body: formData.toString(),
    json: true,
  }
  );
};


const getUserUnlockToken = async (username, password) => {
  const userLoginUri = `${scheme}://${host}/auth/realms/${realm}/protocol/openid-connect/token`;
  const response = await fetch(
    userLoginUri,
    userLogsInOptions(username, password),
  );
  const responseJson = await response.json();
  console.log('acces_token ', responseJson.access_token);
  if (responseJson.error) {
    console.error('error ', responseJson.error);
  }
  console.log('json ', responseJson);
  return responseJson.access_token;
};

You can use UrlSearchParams and then do a toString() like so:

Here is a simple way of doing it:

fetch('https://example.com/login', {
    method: 'POST',
    headers: {
        'Content-Type': 'application/x-www-form-urlencoded; charset=UTF-8'
    },
    body: new URLSearchParams({
        'userName': '[email protected]',
        'password': 'Password!',
        'grant_type': 'password'
    })
    .toString()
})
.then(res => {
    //Deal with response:
})

No need to use jQuery, querystring or manually assemble the payload. URLSearchParams is a way to go and here is one of the most concise answers with the full request example:

fetch('https://example.com/login', {
  method: 'POST',
  body: new URLSearchParams({
    param: 'Some value',
    anotherParam: 'Another value'
  })
})
  .then(response => {
    // Do stuff with the response
  });

The same technique using async / await.

const login = async () => {
  const response = await fetch('https://example.com/login', {
    method: 'POST',
    body: new URLSearchParams({
      param: 'Some value',
      anotherParam: 'Another value'
    })
  })

  // Do stuff with the response
}

Yes, you can use Axios or any other HTTP client library instead of native fetch.

var details = {
    'userName': '[email protected]',
    'password': 'Password!',
    'grant_type': 'password'
};

var formBody = [];
for (var property in details) {
  var encodedKey = encodeURIComponent(property);
  var encodedValue = encodeURIComponent(details[property]);
  formBody.push(encodedKey + "=" + encodedValue);
}
formBody = formBody.join("&");

fetch('http://identity.azurewebsites.net' + '/token', {
  method: 'POST',
  headers: {
    'Accept': 'application/json',
    'Content-Type': 'application/x-www-form-urlencoded'
  },
  body: formBody
})

it is so helpful for me and works without any error

refrence : https://gist.github.com/milon87/f391e54e64e32e1626235d4dc4d16dc8

You can use FormData and URLSearchParams to post as application/x-www-form-urlencoded with the example below:

If you have a form:

<form>
    <input name="username" type="text" />
    <input name="password" type="password" />
    <button type="submit">login</button>
</form>

You can add use the JS below to submit the form.

const form = document.querySelector("form");

form.addEventListener("submit", async () => {
    const formData = new FormData(form);
    try {
        await fetch("https://example.com/login", {
            method: "POST",
            headers: {
                "Content-Type": "application/x-www-form-urlencoded",
            },
            body: new URLSearchParams(formData),
        });
    } catch (err) {
        console.log(err);
    }
});

*/ import this statement */
import qs from 'querystring'

fetch("*your url*", {
            method: 'POST',
            headers: {'Content-Type': 'application/x-www-form-urlencoded;charset=UTF-8'},
            body: qs.stringify({ 
                username: "akshita",
                password: "123456",
            })
    }).then((response) => response.json())
      .then((responseData) => {
         alert(JSON.stringify(responseData))
    })

After using npm i querystring --save it's work fine.

Just Use

import  qs from "qs";
 let data = {
        'profileId': this.props.screenProps[0],
        'accountId': this.props.screenProps[1],
        'accessToken': this.props.screenProps[2],
        'itemId': this.itemId
    };
    return axios.post(METHOD_WALL_GET, qs.stringify(data))

If you are using JQuery, this works too..

fetch(url, {
      method: 'POST', 
      body: $.param(data),
      headers:{
        'Content-Type': 'application/x-www-form-urlencoded'
      }
})

According to the spec, using encodeURIComponent won't give you a conforming query string. It states:

1. Control names and values are escaped. Space characters are replaced by +, and then reserved characters are escaped as described in [RFC1738], section 2.2: Non-alphanumeric characters are replaced by %HH, a percent sign and two hexadecimal digits representing the ASCII code of the character. Line breaks are represented as "CR LF" pairs (i.e., %0D%0A).
2. The control names/values are listed in the order they appear in the document. The name is separated from the value by = and name/value pairs are separated from each other by &.

The problem is, encodeURIComponent encodes spaces to be %20, not +.

The form-body should be coded using a variation of the encodeURIComponent methods shown in the other answers.

const formUrlEncode = str => {
  return str.replace(/[^\d\w]/g, char => {
    return char === " " 
      ? "+" 
      : encodeURIComponent(char);
  })
}

const data = {foo: "bar߃©˙∑  baz", boom: "pow"};

const dataPairs = Object.keys(data).map( key => {
  const val = data[key];
  return (formUrlEncode(key) + "=" + formUrlEncode(val));
}).join("&");

// dataPairs is "foo=bar%C3%9F%C6%92%C2%A9%CB%99%E2%88%91++baz&boom=pow"

Just set the body as the following

var reqBody = "username="+username+"&password="+password+"&grant_type=password";

then

fetch('url', {
      method: 'POST',
      headers: {
          //'Authorization': 'Bearer token',
          'Content-Type': 'application/x-www-form-urlencoded; charset=UTF-8'
      },
      body: reqBody
  }).then((response) => response.json())
      .then((responseData) => {
          console.log(JSON.stringify(responseData));
      }).catch(err=>{console.log(err)})

You can use react-native-easy-app that is easier to send http request and formulate interception request.

import { XHttp } from 'react-native-easy-app';

* Synchronous request
const params = {name:'rufeng',age:20}
const response = await XHttp().url(url).param(params).formEncoded().execute('GET');
const {success, json, message, status} = response;


* Asynchronous requests
XHttp().url(url).param(params).formEncoded().get((success, json, message, status)=>{
    if (success){
       this.setState({content: JSON.stringify(json)});
    } else {
       showToast(msg);
    }
});

In the original example you have a transformRequest function which converts an object to Form Encoded data.

In the revised example you have replaced that with JSON.stringify which converts an object to JSON.

In both cases you have 'Content-Type': 'application/x-www-form-urlencoded; charset=UTF-8' so you are claiming to be sending Form Encoded data in both cases.

Use your Form Encoding function instead of JSON.stringify.

Re update:

In your first fetch example, you set the body to be the JSON value.

Now you have created a Form Encoded version, but instead of setting the body to be that value, you have created a new object and set the Form Encoded data as a property of that object.

Don't create that extra object. Just assign your value to body.

wrapped fetch in a simple function

async function post_www_url_encdoded(url, data) {
    const body = new URLSearchParams();
    for (let key in data) {
        body.append(key, data[key]);
    }
    return await fetch(url, { method: "POST", body });
}

const response = await post_www_url_encdoded("https://example.com/login", {
    "name":"ali",
    "password": "1234"});
if (response.ok){ console.log("posted!"); }

Here is the code I used to convert FormData into "application/x-www-form-urlencoded" type

const formData = new FormData(form);
const urlSearchParams = new URLSearchParams();

formData.forEach((value, key) => {
  urlSearchParams.append(key, value);
});

fetch('/form', {
    method: 'POST',
    body: urlSearchParams,
})

Posting this in case it helps anyone:

I've been working on the integration with an OAuth2.0 server provided by one of our partners. The vendor's API documentation asks to provide the "Content-Type: application/x-www-form-urlencoded" header on each request. However, while attempting to send a POST request to get the access token, the server kept responding with an HTTP 400 "Invalid request" error. After several tries, I realized that the vendor's OAUTh server seems to be expecting the value of the "redirect_uri" to be unencoded. Therefore, as a workaround, I had to manually encode each value of the payload and leave the "redirect_uri" unencoded.

Here's an example of the code for your reference:

const getAccessToken = () => {
    let payloadEncoded = '';
    payloadEncoded += 'client_id=' + <OAUTH CLIENT ID>
    payloadEncoded += '&client_secret=' + <OAUTH SECRET>
    payloadEncoded += '&grant_type=authorization_code';
    payloadEncoded += '&code=' + <OAUTH CODE>
    payloadEncoded += '&redirect_uri=https://<REDIRECT URI UNENCODED>';

    const options = {
        method: 'POST',
        headers: {
            'Content-Type': 'application/x-www-form-urlencoded;charset=UTF-8',
        },
        body: payloadEncoded
    };

    fetch('https://<OAUTH SERVER HOST>/c2id/token', options)
        .then(response => response.json())
        .then(data => {console.log(data);
        .catch(error => console.error(error));
}

Obviously, I will reach out to the vendor to make the correction on their side.

I hope this helps!