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Lorefnon

Decoupling your frontend development with gulp and http-proxy

In past developers have often relied on backend-specific toolchains for web application frontends. Some examples would be Rails asset pipeline or the legacy ant based toolchain for YUI. However recently node.js based tooling support for frontend technologies has significantly evolved and it is quite viable to use a node.js based toolchain for managing your frontend projects, even if the backend is not node.js, thus keeping the workflow decoupled from the backend.

This has multiple advantages, primary among them being that javascript developers can configure their tools using a language they already are familiar with without relying on server-side developers.

The workflow I outline in this post utilizes gulp and node module http-proxy.

Gulp is a build system. I prefer it over alternative task runners like grunt and mimosa because, as the gulp's website states quite succinctly :

gulp's use of streams and code-over-configuration makes for a simpler and more intuitive build.

A claim that I have found to be true in practice.

The http-proxy library helps us connect with our backend seemlessly and at the same time keep the codebase in a separate project. By configuring a proxy server we can load frontend assets from our local system while route the rest of the requests to a potentially remote backend. This is particularly helpful when we have multiple loosely coupled mini-applications backed by a single monolithic server-side codebase.

An alternative to this would be to configure the backend to support cross origin requests, but this is really unnecessary if eventually the application will be served from the same domain.

Let us say we have a javascript heavy dashboard which we would like to develop in a separate project. Here is the directory structure I'll use. Please note that following this directory structure is not mandatory and is mainly illustrative.

project
  |_ gulpfile.js    # task runner configuration
  |_ dashboard      # generated files go here
  |  |_ css
  |  |_ js
  |_ node_modules   # node.js dependencies are installed here
  |_ package.json   # configuration for node.js packages
  |_ server.js      # proxy server
  |_ src            # source files
     |_ css
     |_ js

When deploying the application we can simply drop the dashboard folder to the web-root of our application eg. the public folder of a Rails application.

Next we illustrate usage of http-proxy module to create a simple proxy server.

// server.js

var httpProxy = require('http-proxy'),
    connect = require('connect'),
    livereload = require('connect-livereload')

var proxy = httpProxy.createProxyServer()

var app = connect()
    .use('/dashboard', connect.static(__dirname+'/dashboard'))
    .use(function(req, res){
        if (req.url.indexOf('dashboard') == -1) {
            proxy.web(req, res, {
                target: 'http://localhost:3000'
            })
        }
    })
    .listen(4000)

Before running the server, install the node.js dependencies:

npm install --save connect http-proxy connect-livereload

What the above script does is simply serve the urls that have dashboard in the url from dashboard folder while directing the rest of the requests to another server, which in case is simply http://localhost:3000

For complex routing we can use some of the routing libraries for node.js but for our example the simple script above works pretty well.

Our gulp tasks go in gulpfile.js. Configuring gulp tasks is fairly simple. While the official documentation is a thorough reference, we illustrate the workflow through some examples. For example creating a task to clean our target js and css folders is as simple as:

var gulp = require('gulp'),
    clean = require('gulp-clean')

gulp.task('clean', function(){
    gulp.src(['./dashboard/js/*', './dashboard/css/*'])
        .pipe(clean())
})

The stream based based approach really shines when we use pre-processors for our js or css files. For example to use stylus for css we can add:

var stylus = require('gulp-stylus')

gulp.task('css', function(){
    gulp.src('./src/css/*.styl')
        .pipe(stylus())
        .pipe(gulp.dest('./dashboard/css'))
})

To manage dependencies with browserify we can have:

gulp.task('js', function(){
    gulp.src('./src/js/index.js')
        .pipe(browserify())
        .pipe(gulp.dest('./dashboard/js'))
})

As I hope is clear, the stream based approach makes configuration fairly simple, intuitive and consistent throughout.

Of course associated packages above like gulp-stylus, gulp-browserify, gulp-clean have to be installed through npm before we can use them.

While we can run gulp js, gulp css, gulp clean etc. from the command line we would probably want to have a default task that we run most of the time:

gulp.task('default', ['clean', 'js', 'css'])

Now running gulp will cleanup the dashboard/js and dashboard/css folders and run our js and css tasks.

To streamline our workflow we configure a watcher which can monitor our files, and run the associated tasks automatically. Writing a simple watcher is as simple as:

gulp.task('watch', function(){
    gulp.watch('./src/js/**/*', ['default'])
})

And why stop here, let us automate browser refreshes too. We can use livereload to automatically reload our browser whenever the files change.

We can add a watcher that notifies the livereload server with changes:

gulp.task('watch', function(){
    var server = livereload()
    gulp.watch('./src/js/**/*', ['default'])
    gulp.watch('./dashboard/**/*')
        .on('change', function(file){
            server.changed(file.path)
        })
})

Please note that we could not have hooked up the callback to the watcher we already had because then it would not guarantee that the pre-processors have actually completed before our browser refreshes. Please never use timers for situations like this.

If you have been using livereload for a while then you probably have the browser extension for livereload. But in case you haven't you can use a middleware for express in the server.js file. This is especially convenient for testing on several browsers.

var app = connect()
    .use(connect.logger('dev'))
    .use(livereload({
        port: 35729
    }))
    .use('/dashboard', connect.static(__dirname+'/dashboard'))
    .use(function(req, res){
        if (req.url.indexOf('dashboard') == -1) {
            proxy.web(req, res, {
                target: 'http://localhost:3000'
            })
        }
    })
    .listen(4000)

35729 is the default port on which livereload server runs. Note that this relieves us from having to add the livereload script in our page manually because the middleware takes care of it for us.

If you use the above configuration, you will soon notice something strange. When we edit a css file our entire page refreshes. If you have used livereload before or have seen the demos you know that this should not happen. It should just transparently reload the css files.

It happens because of the way our gulp tasks are configured. Whenever a file in src directory changes we run both our js and css tasks which cause both js and css files to be regerated and thus prompt livereload to refresh the page.

To remedy this we have to modify the watch handler:

gulp.task('watch', function(){
    var server = livereload()
    gulp.watch('./src/js/**/*.js', ['js'])
    gulp.watch('./src/css/**/*.styl', ['css'])
    gulp.watch('./dashboard/**/*')
        .on('change', function(file){
            server.changed(file.path)
        })
})

If you try now, you will notice that css changes no longer refresh the full page as expected.

While the above was not an indepth introduction to any of the technologies involved, I hope that it gave a basic idea about how node.js based tools can be used for a streamlined frontend development workflow. As always any comment or criticism is welcome.

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Lorefnon

Full stack web developer and polyglot programmer with strong interest in dynamic languages, web application development and user experience design.


Strong believer in agile methodologies, behaviour driven development and efficacy of open source technologies.


© 2013 - 2015 Gaurab Paul


Code licensed under the The MIT License. Content and Artwork licensed under CC BY-NC-SA.


The opinions expressed herein are my personal viewpoints and may not be taken as professional recommendations from any of my previous or current employers.


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