Rediscovering JavaScript

Chaining Promises

One elegant feature of promises is that they form a pipeline like in the functional composition we saw in ​Arrow Functions and Functional Style​. Since both then() and catch() return a promise, calls to these functions may be chained to apply a series of filtering and transformations. An example will help you appreciate this elegance.

In the example in ​No Thanks to Callback Hell​ we used the fs library’s readFile() asynchronous method that relied on callback. The fs-extra library provides a wrapper around the functions of the fs library. We will use that to read the contents of a file asynchronously, but this time using promises instead of callbacks.

Wrapping Callbacks into Promises

fs-extra is a library that wraps the callback-taking ...