Module.exports in node.js (+ testing your npm package!)

In a previous blog post, I discussed the process of creating and publishing an npm package. This will be a post on testing and using your own npm package and further understanding module.exports in node.js.

To use your npm package: (testing w/ node.js)

Install it in your project with npm i @jk-me/practicenpm. You can do this in a new project folder to test your code.

Create a js file (ex. index.js) in the root directory of project.

Import the package into the file and set it to a variable of your choice. const pie = require(‘@jk-me/practicenpm’)

Write code in index.js that uses the functions in the package and console.log the output. In terminal run node index.jsto execute script and see output in the terminal.

const pie = require(‘@jk-me/practicenpm’)         //loads module, w exports.tiny function 
console.log( pie.tiny("a string with spaces") )      //uses exported function from required module
=> 'astringwithspaces'                                    //logged output in terminal

You can also use node (javascript) cli with node command, and .exit to exit

After installing your package in your test project folder, it will appear inside it in the node_modules directory. You can modify your code in here to test it using the above method before actually updating your module and publishing a new version to npm. Of course this is only for testing purposes and you normally wouldn’t modify packages after installing them.

module.exports

Node.js uses a module system, where each file is treated as a separate module. Every JS file has module.exports as a special object by default.

Module.exports is the object returned by a require(‘yourModule’) call of the module in another file. It can be a function itself, a class constructor, an object pointing to multiple functions, or any other value.

Functions and objects are added to the root of a module file by specifying attributes to the exports object. For example, module.exports.myFn = () => alert(‘Hello’)

Exported functions can also be written as

module.exports = {
  addone: function(n) { return n+1 },
  minusone: function(n) { return n-1 }
};

exports is a shortcut for module.exports However, assigning a value to exports itself no longer binds it to module.exports and it will not be exported, so you should also assign that value to module.exports.

Variables local to module files are private. Node.js wraps the module in a function called module wrapper before executing a require statement.

There are 3 types of modules: core, local and third-party. Core modules are included in node.js. They must still be imported (ex. require(‘http’)), Some examples include ’http’, ’path’, and ’querystring’, used to set up Node.js http servers, deal with file paths, and deal with query strings, respectively.

Local modules exist in your local node.js app, and third-party modules are, for example, imported npm packages.

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