Fetch - HTTP POST Request Examples

Below is a quick set of examples to show how to send HTTP POST requests to an API using fetch() which comes bundled with all modern browsers.

Other HTTP examples available:

• Fetch: GET, PUT, DELETE
• Axios: GET, POST, PUT, DELETE
• React + Fetch: GET, POST, PUT, DELETE
• React + Axios: GET, POST, PUT, DELETE
• Angular: GET, POST, PUT, DELETE
• Vue + Fetch: GET, POST, PUT, DELETE
• Vue + Axios: GET, POST
• Blazor WebAssembly: GET, POST

Simple POST request with a JSON body using fetch

This sends an HTTP POST request to the Reqres api which is a fake online REST api used for testing, it includes a generic /api/<resource> route that supports POST requests to any <resource> and responds with the contents of the post body and a dynamic id property. This example sends an article object to the /api/articles route and then writes the id from the response to the #post-request .article-id element so it's displayed on the page.

// Simple POST request with a JSON body using fetch
const element = document.querySelector('#post-request .article-id');
const requestOptions = {
    method: 'POST',
    headers: { 'Content-Type': 'application/json' },
    body: JSON.stringify({ title: 'Fetch POST Request Example' })
};
fetch('https://reqres.in/api/articles', requestOptions)
    .then(response => response.json())
    .then(data => element.innerHTML = data.id );

Example Fetch POST request at https://stackblitz.com/edit/fetch-http-post-request-examples?file=post-request.js

POST request using fetch with async/await

This sends the same POST request using fetch, but this version uses an async function and the await javascript expression to wait for the promises to return (instead of using the promise then() method as above).

(async () => {
    // POST request using fetch with async/await
    const element = document.querySelector('#post-request-async-await .article-id');
    const requestOptions = {
        method: 'POST',
        headers: { 'Content-Type': 'application/json' },
        body: JSON.stringify({ title: 'Fetch POST Request Example' })
    };
    const response = await fetch('https://reqres.in/api/articles', requestOptions);
    const data = await response.json();
    element.innerHTML = data.id;
})();

Example Fetch POST request at https://stackblitz.com/edit/fetch-http-post-request-examples?file=post-request-async-await.js

POST request using fetch with error handling

This sends a POST request with fetch to an invalid url on the api then writes the error message to the parent of the #post-request-error-handling .article-id element and logs the error to the console.

The fetch() function will automatically throw an error for network errors but not for HTTP errors such as 4xx or 5xx responses. For HTTP errors we can check the response.ok property to see if the request failed and reject the promise ourselves by calling return Promise.reject(error);. This approach means that both types of failed requests - network errors and HTTP errors - can be handled by a single catch() block.

// POST request using fetch with error handling
const element = document.querySelector('#post-request-error-handling .article-id');
const requestOptions = {
    method: 'POST',
    headers: { 'Content-Type': 'application/json' },
    body: JSON.stringify({ title: 'Fetch POST Request Example' })
};
fetch('https://reqres.in/invalid-url', requestOptions)
    .then(async response => {
        const isJson = response.headers.get('content-type')?.includes('application/json');
        const data = isJson && await response.json();

        // check for error response
        if (!response.ok) {
            // get error message from body or default to response status
            const error = (data && data.message) || response.status;
            return Promise.reject(error);
        }

        element.innerHTML = data.id;
    })
    .catch(error => {
        element.parentElement.innerHTML = `Error: ${error}`;
        console.error('There was an error!', error);
    });

Example Fetch POST request at https://stackblitz.com/edit/fetch-http-post-request-examples?file=post-request-error-handling.js

POST request using fetch with set HTTP headers

This sends the same POST request again using fetch with a couple of extra headers set, the HTTP Authorization header and a custom header My-Custom-Header.

// POST request using fetch with set headers
const element = document.querySelector('#post-request-set-headers .article-id');
const requestOptions = {
    method: 'POST',
    headers: { 
        'Content-Type': 'application/json',
        'Authorization': 'Bearer my-token',
        'My-Custom-Header': 'foobar'
    },
    body: JSON.stringify({ title: 'Fetch POST Request Example' })
};
fetch('https://reqres.in/api/articles', requestOptions)
    .then(response => response.json())
    .then(data => element.innerHTML = data.id);

Example Fetch POST request at https://stackblitz.com/edit/fetch-http-post-request-examples?file=post-request-set-headers.js