Give Grunt the Boot! A Guide to Using npm as a Build Tool

Front-end build and workflow tools are available in abundance: Grunt, Gulp, Broccoli, and Jake to name but a few. These tools can automate almost anything you find yourself doing repeatedly in a project, from minifying and concatenating source files, to running tests or compiling code. But the question is, do you need them? Do you really want to introduce an additional dependency to your project? The answer is “No!”. There is a free alternative that can do the majority of these tasks for you and it comes bundled with Node.js. Of course I’m talking about npm.

In this article we’ll discuss what npm is capable of as a build tool. If you’d like a quick primer on npm before starting, please refer to our beginner’s guide to npm.

npm Scripts

To start our discussion, we’re going to create a directory for our new demo project, that we’ll call “buildtool”. Once done, we’ll move into this folder and then run the command npm init to create a package.json file:

$ mkdir ~/buildtool && cd ~/buildtool
$ npm init

You’ll be asked several questions. Feel free to skip all or part of them as you’ll replace the final content of the package.json file with the following content:

{
  "name": "buildtool",
  "version": "1.0.0",
  "description": "npm as a build tool",
  "dependencies": {},
  "devDependencies": {},
  "scripts": {
    "info": "echo 'npm as a build tool'"
  },
  "author": "SitePoint",
  "license": "ISC"
}

As you can see, we have a scripts object with a property called info. The value of info is going to be executed in the shell as a command. We can see a list of the scripts properties (also known as commands) and values defined in a project by running the command:

$ npm run

If you run the previous command in our project folder, you should see the following result:

Scripts available in buildtool via `npm run-script`:
  info
    echo 'npm as a build tool'

In case you want to run a specific property, you can run the command:

$ npm run <property>

So, to run the info command we defined in the package.json file, we have to write:

$ npm run info

It’ll produce the following output:

$ npm run info
> buildtool@1.0.0 info /home/sitepoint/buildtool
> echo 'npm as a build tool'

npm as a build tool

If you only want the output of info, you can use the -s flag which silences output from npm:

$ npm run info -s
npm as a build tool

We only used a simple echo so far, but this is a very powerful feature. Everything on the command line is available to us and we can be very creative here. So let’s build on what we’ve covered up to this point and install some packages to create some common workflows.

Workflows

The first thing we would like to implement is a linting capability for our JavaScript files. This involves running a program that will analyse our code for potential errors. We are going to use JSHint for this, so the first step is to install the package via npm:

$ npm install jshint --save-dev

After you execute this command, you’ll see a new subfolder named node_modules. This is where JSHint has been downloaded. In addition, we also need to create the following folder structure for our project:

├── assets
│   ├── css
│   │   └── main.css
│   └── scripts
│       └── main.js
├── dist
├── package.json
├── node_modules
└── test
    └── test.js

On a Unix system, this can be done with the following command:

$ mkdir -p assets/css assets/scripts test && touch assets/css/main.css assets/scripts/main.js test/test.js

Linting

Now we’ll force some syntax errors in the main.js file. At the moment the file is empty, so open it and paste in the following content:

"use strict";

var Author = new function(name){
  this.name = name || "Anonymous";
  this.articles = new Array();
}

Author.prototype.writeArticle = function(title){
  this.articles.push(title);
};

Author.prototype.listArticles = function(){
  return this.name + " has written: " + this.articles.join(", ");
};

exports.Author = Author;

var peter = new Author("Peter");
peter.writeArticle("A Beginners Guide to npm");
peter.writeArticle("Using npm as a build tool");
peter.listArticles();

Hopefully the intent of this code is clear — we are declaring a constructor function whose purpose it is to create new Author objects. We also attach a couple of methods to Author’s prototype property which will allow us to store and list the articles an author has written. Notice the exports statement which will make our code available outside of the module in which it is defined. If you’re interested in finding out more about this, be sure to read: Understanding module.exports and exports in Node.js.

Next, we have to add a property to our scripts object in package.json that will trigger jshint. To do that, we’ll create a lint property as follows:

"scripts": {
  "info": "echo 'npm as a build tool'",
  "lint": "echo '=> linting' && jshint assets/scripts/*.js"
}

Here we’re taking advantage of the && operator to chain the commands and file globs (the asterisk) which gets treated as a wildcard, in this case matching any file with a .js ending within the script directory.

Note: the Windows command line does not support globs, but when given a command line argument such as *.js, Windows passes it verbatim to the calling application. This means that vendors can install compatibility libraries to give Windows glob like functionality. JSHint uses the minimatch library for this purpose.

Now let’s lint the code:

npm run lint -s

This produces the following output:

=> linting
assets/scripts/main.js: line 1, col 1, Use the function form of "use strict".
assets/scripts/main.js: line 5, col 28, The array literal notation [] is preferable.
assets/scripts/main.js: line 3, col 14, Weird construction. Is 'new' necessary?
assets/scripts/main.js: line 6, col 1, Missing '()' invoking a constructor.
assets/scripts/main.js: line 6, col 2, Missing semicolon.
assets/scripts/main.js: line 16, col 1, 'exports' is not defined.

6 errors

It works. Let’s clean up those errors, re-run the linter to make sure, then move on to some testing:

(function(){
  "use strict";

  var Author = function(name){
    this.name = name || "Anonymous";
    this.articles = [];
  };

  Author.prototype.writeArticle = function(title){
    this.articles.push(title);
  };

  Author.prototype.listArticles = function(){
    return this.name + " has written: " + this.articles.join(", ");
  };

  exports.Author = Author;

  var peter = new Author("Peter");
  peter.writeArticle("A Beginners Guide to npm");
  peter.writeArticle("Using npm as a build tool");
  peter.listArticles();
})();

Notice how we have wrapped everything in an immediately invoked function expression.

npm run lint -s
=> linting

No errors. We’re good!

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