EcmaScript Modules

995 words · 5 min read

v01: Basic Example 01

cat ex/ecmascript_modules_ex01.js
## export function addTextToBody(text) {
##   const div = document.createElement('div');
##   div.textContent = text;
##   document.body.appendChild(div);
## }
export function addTextToBody(text) { ... }

Using import inside <script type="module"> tag:

cat ex/ecmascript_modules_ex01.html
## <!doctype html>
## <html lang="en">
##   <head>
##     <meta charset="utf-8">
##     <title>Es Module Demo</title>
##   </head>
##   <body>
##     <main id="js-main" class="main"></main>
##     <script type="module">
##       import {addTextToBody} from './ecmascript_modules_ex01.js';
##       addTextToBody('Modules are pretty cool.');
##     </script>
##   </body>
## </html>
import {addTextToBody} from './ecmascript_modules_ex01.js';
addTextToBody('Modules are pretty cool.');

We have two options to open web page:

  1. We can start a static web server in order to prevent CORS errors:

    python3 -m http.server

    Open web page:

    http://localhost:8000/ex/ecmascript_modules_ex01.html

  2. Or we can open the web page from a static web server such as rawgit:

    https://rawgit.com/mertnuhoglu/study/master/js/ex/ecmascript_modules_ex01.html

v04: Webpack Official Getting Started Tutorial

Following Webpack Getting Started Tutorial, I typed the following commands:

mkdir -p ex/ecmascript_modules_ex04
cd ex/ecmascript_modules_ex04
npm init -y
npm install webpack webpack-cli -D
mkdir src
mkdir dist
npm install --save lodash
cat ex/ecmascript_modules_ex04/src/index.html
## <!doctype html>
## <html>
##   <head>
##     <title>Getting Started</title>
##   </head>
##   <body>
##     <script src="bundle.js"></script>
##   </body>
## </html>
cat ex/ecmascript_modules_ex04/src/index.js
## import _ from 'lodash';
## 
## function component() {
##   var element = document.createElement('div');
##   element.innerHTML = _.join(['Hello', 'webpack'], ' ');
##   return element;
## }
## document.body.appendChild(component());
cp src/index.html dist/index.html
./node_modules/.bin/webpack src/index.js --output dist/bundle.js

Note that, here we don’t generate dist/index.html. Instead we simply copied it from src/index.html. Later, we will use HtmlWebpackPlugin to generate it.

open dist/index.html

Open web page:

https://rawgit.com/mertnuhoglu/study/master/js/ex/ecmascript_modules_ex04/dist/index.html

v05: Configuration File: webpack.config.js

Now, let’s use configuration file to specify parameters of webpack:

I copied everything from ecmascript_modules_ex04 into a new folder

cp -R ex/ecmascript_modules_ex04 ex/ecmascript_modules_ex05
cat ex/ecmascript_modules_ex05/webpack.config.js
## const path = require('path');
## module.exports = {
##   entry: './src/index.js',
##   output: {
##     filename: 'bundle.js',
##     path: path.resolve(__dirname, 'dist')
##   }
## }

Now, we will use configuration settings while running webpack:

cd ex/ecmascript_modules_ex05
./node_modules/.bin/webpack --config webpack.config.js

Open web page:

https://rawgit.com/mertnuhoglu/study/master/js/ex/ecmascript_modules_ex05/dist/index.html

v06: Asset Management

Loading CSS

cp -R ex/ecmascript_modules_ex05 ex/ecmascript_modules_ex06
cd ex/ecmascript_modules_ex06
npm install --save-dev style-loader css-loader

Add style-loader and css-loader to webpack configuration:

cat ex/ecmascript_modules_ex06/webpack.config.js | sed -n '/module:/,/}/ p'
##   module: {
##     rules: [
##       {
##         test: /\.css$/,
##         use: [
##           'style-loader',
##           'css-loader'
##         ]
##       },

Now, we can import css files into the js scripts.

cat ex/ecmascript_modules_ex06/src/style.css
## .hello {
##   color: blue;
## }

To use css in js:

import './style.css'; // +
...
element.classList.add('hello'); // +
cat ex/ecmascript_modules_ex06/src/index.js
## import _ from 'lodash';
## import './style.css'; // +
## import Icon from './icon.png'; // +
## import Data from './data.csv'; // +
## 
## function component() {
##   var element = document.createElement('div');
##   element.innerHTML = _.join(['Hello', 'webpack'], ' ');
##   element.classList.add('hello'); // +
##   var myIcon = new Image();
##   myIcon.src = Icon;
##   element.appendChild(myIcon);
##   console.log(Data);
##   return element;
## }
## document.body.appendChild(component());

Loading Images

npm install --save-dev file-loader

Add to webpack.config.js:

  {
    test: /\.(png|svg|jpg|gif)$/,
    use: [
      'file-loader'
    ]
  }

To load image files inside js:

import Icon from './icon.png'; // +
...
var myIcon = new Image();
myIcon.src = Icon;
element.appendChild(myIcon);

Loading Data

npm install --save-dev csv-loader

Add to webpack.config.js:

  {
    test: /\.(csv|tsv)$/,
    use: [
      'csv-loader'
    ]
  }

To load image files inside js:

import Data from './data.csv'; // +
...
console.log(Data);

Open web page:

https://rawgit.com/mertnuhoglu/study/master/js/ex/ecmascript_modules_ex06/dist/index.html

v07: Output Management

cp -R ex/ecmascript_modules_ex06 ex/ecmascript_modules_ex07
cd ex/ecmascript_modules_ex07
npm install --save-dev html-webpack-plugin

Add HtmlWebpackPlugin to webpack configuration:

const HtmlWebpackPlugin = require('html-webpack-plugin');
...
plugins: [
  new HtmlWebpackPlugin({
    title: 'Output Management'
  })
],

HtmlWebpackPlugin generates dist/index.html.

Cleaning up the /dist folder

npm install --save-dev clean-webpack-plugin

Add CleanWebpackPlugin to webpack configuration:

const CleanWebpackPlugin = require('clean-webpack-plugin');
...
plugins: [
  new CleanWebpackPlugin(['dist']),

Open web page:

https://rawgit.com/mertnuhoglu/study/master/js/ex/ecmascript_modules_ex07/dist/index.html

v08: Development

Using source maps

How to track down errors? Webpack bundles source files into one bundle.js. When an error occurs how are we going to know from which origin file it comes from?

So, we will split our webpack configuration into two: one for development environment, one for production environment.

cp -R ex/ecmascript_modules_ex07 ex/ecmascript_modules_ex08
cd ex/ecmascript_modules_ex08

Add inline-source-map to webpack configuration:

devtool: 'inline-source-map',

Watching Updates in Files

Every time we make a change in some file, we need to run npm run build.

Let’s run this command automatically after each change.

npm install --save-dev webpack-dev-server

Update webpack.config.js

devServer: {
  contentBase: './dist'
}

This setups a static web server for ./dist directory on localhost:8080.

Update package.json

"start": "webpack-dev-server --open",

Run npm start

Open web page: http://localhost:8080

Since these settings are for development purpose, we won’t open this page from static web server.

v09: Hot Module Replacement HMR

HMR allows any file to be updated without refresh or recompiling.

cp -R ex/ecmascript_modules_ex08 ex/ecmascript_modules_ex09
cd ex/ecmascript_modules_ex09

Enabling HMR

cp -R ex/ecmascript_modules_ex08 ex/ecmascript_modules_ex09
cd ex/ecmascript_modules_ex09

webpack.config.js

devServer: {
  contentBase: './dist',
  hot: true
},
...
new webpack.NamedModulesPlugin(),
new webpack.HotModuleReplacementPlugin()

Run npm start

Open web page: http://localhost:8080

v10: Using JQuery

Using jquery and its addin libraries according to the ES module rules is not as simple as it should be.

I follow the instructions given in Webpack 2, jQuery plugins and imports-loader by Stefan Ledin.

Use imports-loader webpack plugin

cp -R ex/ecmascript_modules_ex09 ex/ecmascript_modules_ex10
cd ex/ecmascript_modules_ex10
npm install --save-dev imports-loader
npm install --save jquery

Put jquery addin library chosen.js into src/vendor

tree ex/ecmascript_modules_ex10
## ex/ecmascript_modules_ex10 [error opening dir]
## 
## 0 directories, 0 files

Add imports-loader for jquery to webpack.config.js

  {
    test: /vendor\/.+\.(jsx|js)$/,
    use: [
      'imports-loader?jQuery=jquery,$=jquery,this=>window',
    ]
  },

Add import statements for jquery and its plugins to index.js

import {$, jQuery} from 'jquery';
window.$ = $;
window.jQuery = jQuery;
import "./vendor/chosen.jquery.min";

Run npm start

Open web page: http://localhost:8080

Source code in https://github.com/mertnuhoglu/study/js/ex/ecmascript_modules_ex10/

v11: Using JQuery 02

Try ProvidePlugin

I follow the instructions given in Webpack Documentation.

Use ProvidePlugin webpack plugin

cp -R ex/ecmascript_modules_ex10 ex/ecmascript_modules_ex11
cd ex/ecmascript_modules_ex11
rm -rf node_modules
npm install --save-dev html-webpack-plugin
npm install
new webpack.ProvidePlugin({
  $: 'jquery',
  jQuery: 'jquery'
})

Now, we can use $ anywhere in the scripts.

Source code in https://github.com/mertnuhoglu/study/js/ex/ecmascript_modules_ex11/

 Tech    13 Mar, 2018

Any work (images, writings, presentations, ideas or whatever) which I own is always provided under
Creative Commons License Creative Commons Attribution-Share Alike 3.0 License

Mert Nuhoglu is a Trabzon-born programmer and data scientist.

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