Clean Code in JavaScript

Native asynchronous APIs

Nowadays, it's normal to expect APIs within a browser and server to provide non-blocking asynchronous ways to call native mechanisms. Common examples of such APIs include the following:

• The DOM Event API, enabling code such as window.addEventListener('click', callback)
• The Node.js file API, enabling code such as fs.readFile(path, callback)
• The Browser Fetch API, enabling code such as fetch().then(callback)

All such interfaces share something in common: they all provide a way to somehow listen for their completion. Usually, this is achieved via a provided callback (a function). This callback will be called at some later point when the task has completed. Similarly, some native APIs return promises, which enable ...