Friday, October 18, 2013

Reusable javascript modules with Bower

In a previous post I have used require.js to download javascript files and optimize them.
Here I'll introduce a useful tool to manage your javascript and css assets. But first of all let's talk about modules definition in Javascript.

Universal module definition

At the moment there is no standard way to define a module (we are waiting for EcmaScript6) but you can easily define your module in a way compatible with AMD, UMD and regular script import. Just pick one of these snippets. I recommend to use one of those because declaring object in the global namespace is not a good practice and libraries like requirejs can help to load and optimize your scripts.


Bower is a package manager designed for the web. You can install it using:

npm install -g bower

And then start downloading your first package (jquery for example):

bower install jquery

You'll find jquery in the jquery folder inside the "bower_components" folder. Bower packages are versioned so you could (and should) specify what version install.
bower install jquery#1.10.2
If this package has some dependencies (other bower packages of course) those will be installed in the same "bower_components" folder. For those who are using node.js: be aware that it is quite different from how npm works! In this case all the dependencies are resolved and flatten in the same folder.

Bower package

A bower package, in fact, is a simple folder with a bower.json file:
  "name": "mypackage",
  "version": "0.0.1",
  "main": [
  "homepage": "",
  "authors": [
    "Donald Duck "<>";
  "description": "an example package",
  "keywords": [
  "license": "private",
  "private": true,
  "ignore": [
  "dependencies": {
    "lodash": "~1.3.1",
Let's see the most important fields:

name: the name of the package

version: the version of the package. It should be the same of the tag on git.

main: these are the main files of your project. For example a jquery repository has a lot of stuff (unbuilded file, test, fixtures etc.) but the main file is just jquery.js.

dependencies: an array of bower packages needed to run this one. You should always specific the version using this syntax.

Bower repository

The published packages are just git tags with a bower.json. The bower command  anyway uses a central repository to store the metadata (name, url of repository, keywords etc.). This repository is on If you have a public project you can publish on the central repository using:
bower register mypackage
The versions available will be taken from the available tags on you repo.

Running your own repository

Let's say you are working on a project and you don't want to share every package you are working on.
You can easily set up your own bower registry and configure bower to use it. You can do this putting a ".bowerrc" in your working directory (or in your home):
    "registry": {
        "search": ["", ""],
        "register": ""

This instructs bower to download packages from your server or the official one (the first has the priority), and to register the packages on your server only.

Automate everything !

Using grunt-bower-task you can create a build step that install all the dependencies required by your bower.json and copy all the files defined in "main" in a folder. If you use require.js you can also use grunt-bower-requirejs to build  the require.js configuration automatically.

I think this is enough to start working with bower. Enjoy!