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 provides both synchronous and asynchronous functions to read files. In the displayFileContent() ...