Rediscovering JavaScript

No Thanks to Callback Hell

Any method that does not return instantaneously should be asynchronous. The traditional approach to designing asynchronous functions relied on callbacks. Let’s take a look at a small example and discuss the issues with this approach.

promises/readfile.js

​const​ fs = require(​'fs'​);

​const​ displayFileContent = ​function​(pathToFile) {
  ​const​ handleFile = ​function​(err, contents) {
    ​if​(err) {
      console.log(err.message);
    } ​else​ {
      console.log(contents.toString());
    }
  };

  ​try​ {
    fs.readFile(pathToFile, handleFile);
  } ​catch​(ex) {
    console.log(ex.message);
  }
};

We first bring in the fs library that ...