readme.md

Node Lessons

Lesson 5: Split our single-file application into different modules

Description When an application becomes larger, keeping everything is one large file makes things messy quickly. In order to improve the readability of the code, and thus the maintenability of the whole application, it is useful to split the code into different files, i.e. modules.

Let's put the code of the request logging into libraries/fileLogger.js and the code which saves the results to file into libraries/dataLogger.js. Those modules will then be loaded by our main index.js file.

Goals

• Move the Data Logger and the File Logger into separated files

Allowed Npm Packages

• axios: http client used to perform http requests
• express: web server
• moment: date manager
• winston: logger

Requirements

• The results must be saved in userdata/data.json
• The logs must be saved under storage/logs/nodeJobs.log
• The Data Logger must reside into libraries/dataLogger.js
• The File Logger must reside into libraries/fileLogger.js

Suggestions

• In order for a module to be imported through require('./myfile'), and have a method which returns a Promise, the module file structure must be the following

// myfile.js

const myFeature = {
  /**
   * Does something.
   *
   * @param {string} data
   * @return {Promise}
   */
  do (data) {
    return new Promise((resolve, reject) => {
      // Do some operation
      resolve(data);
    })
  }
};

module.exports = myFeature;

it can then be imported through const myFeature = require('./myfeature.js') and used with myFeature.do(data), which will indeed return a Promise.