📓 Bundling JavaScript

Let's update our shape tracker application to use import and export statements. By the end of this lesson, we will be using webpack to bundle all of our JavaScript files for us.

Remember, bundling JavaScript is webpack's core functionality. Bundling other modules like CSS, images, and other assets is made possible through loaders, which we'll begin to incorporate in the next lesson!

Bundling JavaScript

First, let's start by adding a dist directory. Next, move index.html inside the dist directory. If you already have a dist directory in your project, simply move index.html inside of it.

Locating your HTML file within the dist directory is the basic setup for a project that uses webpack. However, for us this will be a temporary change. We will be moving index.html back to the src directory in a few lessons when we implement a plugin that directs webpack to create an output HTML file based on a template we provide.

By the way, don't forget that we've added dist/ to our .gitignore file. If we were to push our updated code, changes to index.html wouldn't get pushed. This is fine because this change is temporary — and there is no need to commit our code just yet. However, if you did want to explore using a basic webpack setup in the future, you'd want to update your .gitignore file to only ignore dist/bundle.js and not the entire directory and HTML.

Here's our current project structure:

shape-tracker/
├── dist
│   ├── index.html
├── src
│   ├── index.js
│   └── triangle.js
├── css
│   └── styles.css
├── package.json
└── .gitignore

Note that we aren't including automatically generated files and directories like node_modules and package-lock.json in the structure above. We're only including the files and directories that we need to add manually.

Adding `import` and `export` Statements

Next, let's update our JavaScript files to use import and export statements. We'll use a default export for Triangle because it's the only thing we'll export from the file.

src/triangle.js

export default function Triangle(side1, side2, side3) {
  ...
}

...

Now we need to make sure we import our Triangle constructor at the top of index.js:

src/index.js

import Triangle from './triangle.js';
...

Updating `index.html`

Finally, we'll make some small updates to the <head> of index.html:

...
<head>
  <script type="text/javascript" src="bundle.js"></script>
  <link rel="stylesheet" href="./../css/styles.css">
  <title>Shape Tracker</title>
</head>
...

Now we only have one JavaScript tag — for bundle.js. That file doesn't exist yet, and that's because webpack creates it for us.

We've also updated the relative path to our stylesheet to ./../css/styles.css. That's because we've moved index.html to our dist folder, and we now have to go out of the dist folder in order to get to the css directory to access styles.css. Take note of a few things:

Two dots /../ in a path indicates that we are moving up a level from the directory we are in, while one dot ./ in path indicates our current working directory.
So the full path ./../css/styles.css says, to load the CSS in styles.css:
- Start in this directory ./
- Then move up a directory /../ — this is the project's root
- Then go into the /css/ directory
- Then locate styles.css

Note that this path will change again in the next lesson when we use webpack to bundle our CSS.

Running webpack

Now run $ npm run build in the root directory of the project to invoke webpack to do its job and bundle our JavaScript files.

webpack will start by accessing the entry point at src/index.js. Then, webpack will recursively add any dependencies (anything that needs to be imported from elsewhere). Since index.js only imports Triangle from triangle.js and triangle.js has no imports of its own, our project currently only has one dependency.

If all goes well, your output will look something like this:

> shape-tracker@1.0.0 build /Users/staff/Desktop/shape-tracker
> webpack

Hash: 7d88ba320f665950d074
Version: webpack 4.46.0
Time: 70ms
Built at: 06/01/2022 9:33:20 AM
    Asset      Size  Chunks             Chunk Names
bundle.js  1.27 KiB       0  [emitted]  main
Entrypoint main = bundle.js
[0] ./src/index.js + 1 modules 650 bytes {0} [built]
    | ./src/index.js 443 bytes [built]
    | ./src/triangle.js 207 bytes [built]

Note: If you get errors, you probably missed a step from previous lessons. Make sure you've actually added a webpack.config.js file with a configuration and updated the scripts section of package.json to include "build": "webpack --mode=development".

Just like with before, we we'll see that webpack creates a bundle.js file in the dist folder. If we look inside of it, we'll see the code from both index.js and triangle.js. This means that webpack has done it's job to concatenate our files together.

The code inside of bundle.js is NOT minified. That's because we've configured webpack to build its bundle in development mode. Minifying code is not as important for development as being able to look through the bundle and debug any code within. We'll revisit the topic of debugging in an upcoming lesson.

Now we can open our index.html file in the browser and our code will work. Woo-hoo!

One important detail to note is that if we go to the console and check the window object, we'll no longer see Triangle just hanging out in the global scope. We can also verify this by typing in the following:

> window.Triangle;
undefined

Our JavaScript code is now modularized and code is scoped where it is needed. This is particularly important as our projects get larger.

So far, we haven't reduced our code much — all we've done is remove a single script tag from our code. However, it's a big deal when a project has hundreds of dependencies. More importantly, our JavaScript logic is separated in different files — which is great for human organization — but then bundled into one file — which is great for speed and efficiency.

We've barely scratched the surface of what webpack can do. In the next several lessons, we'll bundle our CSS, customize webpack for linting, and set up a live development server.