FED

现代网站和应用中另一个常见的任务是从服务端获取个别数据来更新部分网页而不用加载整个页面。这看起来是小细节却对网站性能和行为产生巨大的影响。所以我们将在这篇文章介绍概念和技术使它成为可能，尤其是 Fetch API。

XMLHttpRequest（XHR）对象用于与服务器交互。通过 XMLHttpRequest 可以在不刷新页面的情况下请求特定 URL，获取数据。这允许网页在不影响用户操作的情况下，更新页面的局部内容。XMLHttpRequest 在 AJAX 编程中被大量使用。

Fetch API 提供了一个获取资源的接口（包括跨网络通信）。对于任何使用过 XMLHttpRequest 的人都能轻松上手，而且新的 API 提供了更强大和灵活的功能集。

A modern replacement for XMLHttpRequest

Which Ajax API is best for your application? In this article, we'll examine the pros and cons of the ancient XMLHttpRequest and its modern Fetch API equivalent.

Despite having the word “XML” in its name, it can operate on any data, not only in XML format. We can upload/download files, track progress and much more.

All modern browsers have a built-in XMLHttpRequest object to request data from a server.

JavaScript Fetch API

There’s an umbrella term “AJAX” (abbreviated Asynchronous JavaScript And XML) for network requests from JavaScript. We don’t have to use XML though: the term comes from old times, that’s why that word is there. You may have heard that term already.