Why Switch to Fetch API? A Frontend Guide to Modern AJAX

Introduction

Traditional Ajax relies on XMLHttpRequest (XHR) to send requests and retrieve data, often ignoring separation of concerns. The Fetch API, built on Promises, was created to address XHR’s shortcomings.

XHR Example

Using XHR to send a JSON request typically involves verbose configuration and callback handling.

Fetch Example

Fetching data with the modern API simplifies the code and returns a Promise.

ES6 Syntax

Using ES6 syntax with Fetch further reduces boilerplate.

Handling text/html Responses

Fetch can process text/html responses directly.

Accessing and Setting Headers

Fetch provides methods to read and modify response headers.

Submitting Forms and JSON Data

Form submissions and JSON payloads are straightforward with Fetch.

Fetch Features

Concise, semantic syntax.

Built on standard Promise, supports async/await.

Isomorphic usage via isomorphic‑fetch.

Compatibility

Browser support varies; polyfills are often required.

Native support is limited; use polyfills such as es5‑shim for IE8, es6‑promise, fetch‑polyfill, fetch‑jsonp, and enable Babel runtime for async/await.

Common Issues

Fetch does not send cookies by default; set

credentials: 'include'

.

HTTP 400/500 responses do not reject the promise; only network failures trigger rejection.

Conclusion

Fetch API appears simple but reflects continuous enhancements in JavaScript syntax. Projects often rely on libraries to solve low‑level problems, leading to neglect of underlying API changes. Developers should stay aware of core API evolution and implementations.