Lab: Error Handling

• In this lab, we customize the launch NodeJS app via package.json and develop error handling code in Express controller.
• You can begin the lab via the start directory of Lesson 11 source code
• You can cross check the final result in the finish directory.

Step 1: Custom launch

• Edit the package.json file and modify the script section as follows:

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"scripts": {
  "test": "echo \"Error: no test specified\" && exit 1",
  "start": "node main.js"                                     1
},
 

• With this customization, you can run the commands such as node test and node start to launch your server app.
• Run node test to confirm that no test is specified at the moment.

Step 2: Error handling in Express

• By default, Express.js handles any errors at the end of processing a request.

Error handling approaches with Express

1. Logging to console (console.log) whenever an error occurs.
2. (Recommended) Creating a new controller and install the http-status-codes package

Setup error controller

• Install http-status-codes

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npm install http-status-codes --save
 

• Create errorController.js in the controllers folder with the following contents (Listing 11.2 from the book)

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"use strict";

const httpStatus = require("http-status-codes");

exports.logErrors = (error, req, res, next) => {
  console.error(error.stack);
  next(error);
};

exports.respondNoResourceFound = (req, res) => {
  let errorCode = httpStatus.NOT_FOUND;
  res.status(errorCode);
  res.send(`${errorCode} | The page does not exist!`);
};

exports.respondInternalError = (error, req, res, next) => {
  let errorCode = httpStatus.INTERNAL_SERVER_ERROR;
  console.log(`ERROR occurred: ${error.stack}`);
  res.status(errorCode);
  res.send(`${errorCode} | Sorry, our application is experiencing a problem!`);
};
 

• respondNoResourceFound: missing resources
• respondInternalError: resource processing caused a server-side error

Exercise

• Look at the main.js in Lesson 11 and compare that with main.js in Lesson 10.
• Examine the additional middleware layer added to handle error

Exercise

• Play with the static HTML file in the public directory inside finish and see the responses.

Step 3: Capstone Lab

• Follow the instructions in Lesson 12: Capstone to wrap up Unit 2.