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NodeJS Modules: Imports and Exports - Exercises

Setup

  • Create a new folder.
  • Add a main.js file to the folder.

Math Module

  • Add a math-module.js file to your folder
  • In the math-module.js file add a function called sum. The sum function should take two arguments and return their sum.

Example:

sum(3, 6); //returns 9
  • Add a module.exports statement at the bottom of the math-module.js file.
  • Add the sum function to module.exports.
  • In the main.js file, use the require keyword to import the math-module.js file.
  • Call the sum function from the main.js file and save the result to a new variable.
  • Add a console.log statement that logs the saved variable.
  • Open the terminal and run the main.js file. You should see the output from the sum function
  • Add three more functions to the math.module.js file:
  1. A multiply function (takes two arguments and returns their product).
  2. A divide function (takes two arguments and returns the first argument divided by the second).
  3. A square function (takes one argument and returns its square).

Examples:

multiply(2, 5); //returns 10
divide(20, 10); //returns 2
square(5); //returns 25
  • Add the multiply, divide, and square functions to module.exports in the math-module.js file.
  • In the main.js file, use the use the imported math-module.js file to call the three new functions, and save the results as new variables
  • Log the saved variable.
  • Open the terminal and run the main.js file. You should see the output from all the functions.

String Module

  • Create a new file called strings-module that contains at least three string functions (for example: return the first letter of a string, reverse a string, etc.) of the choosing.
  • Import the string-module into the main.js file and try calling and logging the functions from string-module.
  • Can you also import the string-module into the math-module and use it in there? Or vice versa?

Modular: Files By Extension

The following is a code for an program that takes a user's input of a folder and an extension, and lists all the files in that folder that have the given extension.

const fs = require('fs')
const path = require('path')

const folder = process.argv[2]
const ext = '.' + process.argv[3]

fs.readdir(folder, (err, files) => {
  if (err) {
    console.error(err);
    return;
  }

  files.forEach((file) => {
    if (path.extname(file) === ext) {
      console.log(file)
    }
  })
})

In a new folder, create the files filterFiles.js and main.js.

  1. Paste the above code into filterFiles.js and rewrite it as follows:
  • Do not take any input from the user (i.e. remove lines that make use of the process object).
  • Wrap the code in a function that takes as arguments a folder name, an extension, and a callback function.
  • If there is an error while reading the folder, invoke the callback with the error.
  • Otherwise, invoke the callback at the bottom of the function with two arguments: null and the list of files.
  • Export the function using module.exports.
  1. In main.js do the following:
  • Import the function from filterFiles.js as filterFilesFn.
  • Read the input for folder and extension from the user (using the process object).
  • invoke the function with the following arguments:
    • the folder
    • the extension
    • a callback function that takes as arguments an error object and a list. If the error object is not null, it logs the string: 'there was an error' followed by the erro. Otherwise, it loges the list, with each element in a separate line.