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Gulp — an easy frontend build step

Gulp is my favorite task runner, because it is the essence of simplicity. There is really nothing better for taking care of the repetitive tasks that are converting, concatenating and minifying your assets and resources.

Before we get our hands dirty, let me quickly explain what a task runner is. Actually it is pretty straight forwards, a task runner is a very simple (command line) tool to run common tasks for you. So, what are tasks? A task can be nearly anything: converting your less to css, minifying your javascript, optimizing your svgs, creating an svg sprite or a combination of the before mentioned.

For this example we will be creating a task that watches our less files and whenever we change them, converts the less files to css, adds all needed vendor-prefixes and combines the bunch.

Install npm

First we need to get a tool to install gulp, this tool is npm, the node package manager. Installing it is as easy as downloading the installer and running it.

Now you should be able to get the current npm version by running npm -v in your terminal app. You can update npm via npm, with the following command in your terminal.

sudo npm install npm -g

cd into your project so we can start setting it up.

# move to the folder where you store all your projects cd ~/Code # create a new folder if you haven't already mkdir newProject # move into the new folder cd newProject

Now we need to initialize npm by running npm init --yes. This will create a new package.json file for us, which will be used to track the gulp packages we install. If you are building a website without using node, all that really matters are the devDependencies but you can update this file if you wish, mine looks like this.

{ "name": "project name", "version": "1.0.0", "description": "Your projects description", "main": "index.js", "dependencies": {}, "devDependencies": {}, "scripts": { "test": "echo \"Error: no test specified\" && exit 1" }, "author": "Lukas Oppermann", "license": "MIT" }

TIP: Check in the package.json into git, so when anyone clones down the repository, a simple npm install will download and install all your dependencies.

Install gulp

Perfect! Now that we have npm up and running lets get into gulp. We need to install gulp globally and as a local dependency in our project. This is a special gulp thing, and not really important, so I won't go into it the whys. Always add the --save-dev flag to automatically save the dependencies to the package.json file.

# install gulp globally npm install --global gulp # install gulp in your project # make sure to cd into your project first npm install --save-dev gulp

Your package.json should now have gulp within the devDependencies section. The number after the colon is the installed version. This might differ for you, depending on the current gulp version.

"devDependencies": { "gulp": "^3.9.0", },

Moving on, we need to create a gulfile.js in the root of our project to contain all our gulp tasks.

# create an empty gulpfile.js touch gulpfile.js # open gulpfile.js via the terminal or by opening it in finder open gulpfile.js

Open up the gulfile.js in your editor of choice. As the extension .js suggests, this is a normal javascript file, so if you know how to write javascript, you know how to work in this file. If not, don't worry, it's easy.

// we need to load gulp, since we are running npm, we can use the require function var gulp = require('gulp'); // creating our first task // you give a task any name (first argument), it will be used when running the task from the terminal like: gulp compile-less gulp.task('compile-less', function() { // within this function we will define what the task does });

Creating the first task

Now we can start to write the actual jobs the task has to perform, but first we need to install and load all plugins we require for it. You can find plugins on npm.js. Our first step is to convert our .less files to .css and combine them into one. For this we need two plugins: gulp-less will be used to convert our .less and gulp-concat will be used to combine our css into one file.

# you can install multiple npm modules at once like this: npm install --save-dev gulp-less gulp-concat

After adding the two new modules your gulpfile.js should look like the one below.

var gulp = require('gulp'); var less = require('gulp-less'); var concat = require('gulp-concat'); gulp.task('compile-less', function() { // every task needs to return something // using gulp.src we can read all files with // a .less extension from a given directory return gulp.src('./resources/less/*.less') // once we have our files we use the .pipe function, // it takes another function as an argument, gulp plugins // come as functions, so less is the variable name we defined above .pipe(less()) // just as above we now use the concat plugin, it takes an // argument, which is the filename of our combined css .pipe(concat('app.css')) // lastly we use gulp.dest to write the to the file system // the argument is the path at which the file is stored .pipe(gulp.dest('public/css')); });

With this our first gulp task is done. You can use it by running gulp compile-less from your terminal. Afterwards a file named app.css should be created within public/css (or where ever you decided to have gulp save it).

Extending our task

With the basics working, we will add the autoprefixer to our task. If you use css like animation, this plugin will automatically prefix it for the browsers you specified. First we need to download the plugin for it.

npm install --save-dev gulp-autoprefixer

Once this is done we add the plugin to our gulpfile.js and use the autoprefixer within a pipe statement.

var gulp = require('gulp'); var less = require('gulp-less'); var concat = require('gulp-concat'); var autoprefixer = require('gulp-autoprefixer'); gulp.task('compile-less', function() { return gulp.src('./resources/less/*.less') .pipe(less()) .pipe(concat('app.css')) // the autoprefixer function takes an object as an argument // which lets you define which versions you want to support .pipe(autoprefixer({ browsers: ['last 2 versions', 'IE 9', 'IE 8'], cascade: false })) .pipe(gulp.dest('public/css')); });

The default task

The default task is a somewhat special task in gulp, you create it by simply naming a task default. The special part about this task, is that you can call it by simply typing gulp without any argument into the terminal. Obviously this should be used for your most common task. In your gulpfile.js create the default task to call the compile-less task.

// instead of a function, you can also provide an array as the tasks' argument // if you do this, all tasks in this in the array will be run gulp.task('default', ['compile-less']);

Watch your files

With your less files you probably want to compile them after every change which is very annoying, if done by hand. Luckily there is a way to avoid this, the watch task. Create a watch task that compiles all less files, once you change one is as easy as writing a normal task. We will just facilitate the watch method on the gulp object to tell us when a file changes, and run the appropriate task.

// a watch task keeps an eye on the files specified as the first argument // and runs the tasks from the second argument on change gulp.task('watch-less', function(){ gulp.watch(['./resources/less/*.less'], ['compile-less']); });

If you now run gulp watch-less from the terminal your files will be recompiled the next time you save them. Beware: When adding new files you need to stop the watcher ctrl + c and restart it by running gulp watch-less. There is one annoyance left: You need to actively trigger the watch task. But we can help this, by simply appending it to your default array.

// now gulp will compile our less files and start the watch task // when we run gulp in the terminal gulp.task('default', ['compile-less', 'watch-less']);

This is it, for our first dive into gulp. It may seem a little complicated, but it is just basic javascript. Once you get used to it for a while it will be easy to whip up new tasks and when you go back to a project without gulp you will loathe the many manual steps you have to do.