Packages

Node Js works off of the concept that you can create and share Js files, that can be grouped into "packages". Theses "packages" work similar to Python "modules" in that you import the "modules" you wish to use. More information about Node modules and packages can be found here.

You're not limited to packages that others have created, you can create them on your own. In order to create a package you need to be able to import and export files and folders. We can demonstrate the concept by creating a package that we can "share" with another Js file. We're going to create a Js file called [math.js]. Inside this file, all we are going to have is two functions, and one variable assignment.

Here is the file contents:

• JavaScript
• math.js
• • const add = ( x, y ) => x + y;
  • const square = x => x * x;
  • const PI = 3.14159;

So we've created a Js package that we can import into our other Js files. For that, we're going to need another Js file to work with. We'll call it [app.js]. Now in our new [app.js], we need to "import" our [math.js], and to do that, we use require like so:

• JavaScript
• app.js
• • const mathImp = require ('./math');
  • console.log(mathImp);

Now if we run this in our "node" console, what will we get?

• Node Terminal
  • node app.js

• { }

We do that with module.exports, like so:

• JavaScript
• math.js
• • const add = ( x, y ) => x + y;
  • const square = x => x * x;
  • const PI = 3.14159;

• module.exports.add = add;
  module.exports.square = square;
  module.exports.PI = PI;

And now, if we run our [app.js], we now get:

• { add: [ Function: add ], square: [ Function: square ], PI: 3.14159 }

So now, from within [app.js], we can log out some results from our [math.js], by adding:

• JavaScript
• app.js
• • // assign variables to the [math.js] objects
  • const {add, square, PI} = require ('./math')
  • // log the objects with the provided values
  • console.log(add( 2, 2 ));
  • console.log(square(5));
  • console.log(PI);

and we get:

• 4
• 25
• 3.14159

Simplifying the Code

We can simplify our "exports" code in our [math.js] file by creating an object and exporting the object file like so:

• const math = {
  • add: add,
  • square: square,
  • PI: PI
• }
• module.exports = math;

Another way to simplify the code would be to export each "math" item directly, like so:

• module.exports.add = ( x, y ) => x + y;
• module.exports.square = x => x * x;
• module.exports.PI = 3.14159;

In Summary

So we can "import packages" into another Js file by using the require keyword, in the file that we are importing into.

• const variable = require ('./file to import');

We can only import items that have been exported in the originating package with the module.exports keyword, eg:

• module.exports.add = ( x, y ) => x + y;

Final Code

• JavaScript
• math.js
• • // export our math objects
  • module.exports.add = ( x, y ) => x + y;
  • module.exports.square = x => x * x;
  • module.exports.PI = 3.14159;

• JavaScript
• app.js
• • // import our math objects
  • const {add, square, PI} = require ('./math');
  • // log the results
  • console.log(add(2, 2));
  • console.log(square(5));
  • console.log(PI);

• 4
• 25
• 3.14159

One Last Note

Now, one other note about imports. We can also import an entire folder of files. To do this you need to create your packages in a folder, and the create a file that must be named index.html. Lets demonstrate. We'll create a folder called "pets, and inside the folder, we will create three files with different pet information. So in our file structure, we have:

• // pets folder
• pets
• • // pet files
  • chico.js
  • jitters.js
  • jasper.js

So pets is the "parent" folder and contains the three "pet" Js files. The Js file will contain info about each pet. Here is Chico's file:

• JavaScript
• // chico.js
• module.exports = {
  • name: 'Chico',
  • color: 'Brown',
  • type: 'Dog'
• }

So the [chico,js] file has been set up to export info about the "Chico" pet. The other two pet files will be set up exactly the same, but with their specific pet info. And now, within our "Pets" folder, we need to create an "index" file to control the import of all the other files. So we create the new [index.js] inside of our "Pets" folder:

• // pets folder
• pets
• • // pet files
  • chico.js
  • jitters.js
  • jasper.js
  • // add the index controller file
  • index.js

Now, inside our new [index.js] file, we're going to require our three pet files, like so:

• JavaScript
• // index.js
• // import the individual pet files
• const chico = require (./chico);
• const jitters = require (./jitters);
• const jasper = require (./jasper);
• // combine the three files into an array
• const allPets = [ chico, jitters, jasper ];

Now if we run our [index.js], we get:

• [
  • { name: 'Chico', color: 'Brown', type: 'Dog' },
  • { name: 'Jitters', color: 'Brown', type: 'Cat' },
  • { name: 'Jasper', color: 'Black', type: 'Cat' }
• ]

So we can see that we have imported all three pet files as an array. Now lets go ahead and export this array from within our [index.js] file:

• JavaScript
• // index.js
• // export the allPets array
• module.exports = allPets;

and now we can import the entire "pets" folder into our existing [app.js], by adding the following line:

• JavaScript
• // app.js
• const myPets = require ('./pets');

and now if we run our [app.js], we get this output:

• [
  • { name: 'Chico', color: 'Brown', type: 'Dog' },
  • { name: 'Jitters', color: 'Brown', type: 'Cat' },
  • { name: 'Jasper', color: 'Black', type: 'Cat' }
• ]

Lets Recap:

• - We created a new pets folder.
• - Inside this folder we created three individual pet Js files.
  • each file exported info on an individual pet.
• - We then created an [index.js] "controller" file that imports all three pet files
  • we then added the three imports to an array, and exported that array.
• - Finally, we imported our pets folder into our [app.js] file.