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Gulp

Why is this important?

This workshop is important because:

Gulp is a useful tool for automating tasks in order to increase productivity. Today we'll specifically use it mostly for transpiling ES6 to ES5 and Sass into CSS.

What are the objectives?

After this workshop, developers will be able to:

• Write a Gulp task and run it
• Leverage pre-built Gulp plugins

Where should we be now?

Before this workshop, developers should already be able to:

• Implement client & server-side JavaScript.

Introducing Gulp

• Gulp is a software built on Node.
• It runs tasks that manipulate files on your system.
• It is an active, open-source project.
• There are many community-built plugins built to work directly with gulp.
• Among other things, it is commonly used for transcompilation and minificiation to automate your workflow.

Installing Gulp

1. You'll want to install gulp globally. You can do this by running the npm install gulp -g command.
2. We also need to include gulp in our project. To do that, we will run npm install gulp --save-dev. Let's use --save-dev (a production environment should not be concerned with build tools).
3. Now, run gulp!

No gulpfile found

Oops, we ran into an error. Gulp requires that we store our tasks in a gulpfile.js. This should be in the same directory as your package.json. Make that file then run Gulp again.

Using gulpfile ~/path/to/gulpfile.js
Task 'default' is not in your gulpfile
Please check the documentation for proper gulpfile formatting

Another error! Ok, let's solve this problem by defining a Gulp task.

Defining a Gulp Task

• What is a task?
• A task is something we must do to achieve a result.
• In Gulp, we create tasks to perform tasks that can transform our code.
• A task may perform one job; it may also perform many at once.

In our gulpfile.js we need to include the gulp module. To do this, we should define a variable: var gulp = require('gulp'); This will allow us to call upon Gulp to create a task.

First (Default) Task

After declaring our gulp variable, we should create our first task. This will require us to call upon Gulp to define a task. We must also have a name for our task. By default, Gulp requires a default task. It is the first task that Gulp will look for when reading your gulpfile.js. Let's define our first (default) task:

var gulp = require('gulp');

//define a task with the name of 'default'
// and a callback to perform when the task is ran
gulp.task('default', function() {
  console.log('I am the default task. Hear me roar');
});

In your terminal, run gulp. This will have the library look for a default task in your gulpfile.js. It will then execute the callback that you define for your task. The output will appear as follows:

Starting 'default'...
I am the default task. Hear me roar
Finished 'default' after 144 μs

Compiling Sass

Create a new directory sass-to-css and cd into it.

npm init
npm install --save-dev gulp gulp-sass

//gulpfile.js
var gulp = require('gulp');
var sass = require('gulp-sass');

Define a styles task that looks in a /sass directory for all .scss files, logs any errors that occur, and then compiles the result into a /css directory.

gulp.task('styles', function() {
    gulp.src('sass/**/*.scss')
        .pipe(sass().on('error', sass.logError))
        .pipe(gulp.dest('./css/'));
});

Create a /sass directory and touch a main.scss file inside.

Run gulp styles and it will find your .scss file and output a corresponding .css file for you.

Lastly let's add the task we just created to gulp's default task and have it run the task upon file changes by watching the file. Now every time you save, your .scss will trigger the styles gulp task and compile the changes for you!

To do this, at the bottom of your file add:

gulp.task('default',function() {
    gulp.watch('sass/**/*.scss',['styles']);
});

Compiling ES6

We've yet to talk about ES6, aka ECMAScript 2015, but it's the next iteration of JavaScript so let's get a taste for it. It's nice to write in, but not supported everywhere yet. Let's write some ES6 code and compile it to ES5, which is universally supported.

Create a new directory somewhere called es6-to-es5 and cd into it.

Require all the modules we'll be using.

npm init
npm install --save-dev gulp gulp-babel babel-preset-es2015

Create a file for gulp to reference.

touch gulpfile.js

Inside the file do something similar to what we did to transpile our sass. Instead now we'll be using gulp-babel to help us transpile our ES6 to ES5.

Here we'll be creating a task called scripts. It will read in all our ES6 .js files living inside the src directory, pipe them through our babel to transpile them to ES5 and then send the output to corresponding files in the dist directory.

At the very bottom, just like previously, we're creating a default watch task that will execute the scripts task every time any .js file is saved inside our src directory. Pretty neat!

var gulp = require('gulp');
var babel = require('gulp-babel');

gulp.task('scripts', function () {
	return gulp.src('src/**/*.js')
		.pipe(babel({
			presets: ['es2015']
		}))
		.pipe(gulp.dest('dist'));
});

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

Note: Babel is the transpiler we'll be using to convert our ES6 to ES5. babel-preset-es2015 is one of the preset collection of plugins we can use for it. It contains all the features for ES6 packed together, but in theory you could only require es2015-arrow-functions or es2015-classes, for example, if you wish to be more specific.

Let's try out some ES6. Below find some working ES6 code, take a moment to look it over. What are your thoughts?

// define an ES6 class called Person
class Person {
  // define the method to run for each instantiation
  constructor(name, age, type="person") {
    this.name = name
    this.age = age
    this.type = type
  }
  // define a greet method
  greet() {
    return `Hi I'm ${this.name}!`
  }
}

// export the Person class
module.exports = Person

Run gulp in your project's root, then create an app.js file in your src directory and save it. What happened? Also in the root of your project, run node and require the Person class with var Person = require(./dist/app.js).

Note: we are requiring the transpiled ES5 code into node.

Challenge: Can you instantiate a new person?

Exciting stuff! Here's a quick look at some of the new ES6 syntax. Take a moment to review it and then try out this online quiz (open book is fine). It will introduce you to some new ES6 concepts. Feel free to jot down anything that's surprising and we'll discuss it. Feel free to try any of this fancy ES6 stuff out in your src/app.js file.

Additional Notes

• You will need to re-run the gulp command every time you make a change to the gulpfile.js.
• There is nodemon support for gulp.
• As mentioned previously, you can have gulp watch files for changes using gulp-watch.
• You can bundle your multiple files into one output file with gulp-concat.
• And also minify JS or CSS!