adding how-2-js exercise

js/tests/how-2-js_test.js

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+import { readFileSync as read } from 'fs'
+
+// /*/ // ⚡
+
+export const tests = [
+  ({ eq }) =>
+    eq(
+      read('/jail/student/index.html', 'utf8').trim(),
+      '<script type="module" src="hello-world.js"></script>',
+    ),
+  ({ eq }) =>
+    eq(
+      read('/jail/student/hello-world.js', 'utf8').trim(),
+      `console.log('Hello World')`,
+    ),
+]

subjects/how-2-js.en.md

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+## How 2 JS
+
+### Instructions
+
+Hello and welcome to the JS piscine, first you will have to learn
+to execute javascript.
+
+Being a special child, JS can run in different **runtime**, what you can
+do with it greatly depend of your runtime.
+
+Luckly you don't need to install anything for that since all you
+need is a web browser.
+
+> Main runtime for executing JS are: any web browser, NodeJS and Deno.
+
+Let's make a hello world:
+
+```bash
+# first we create the javascript file
+echo "console.log('Hello World')" > how-2-js.js
+
+# To run JS in your browser you need to import it from an HTML page:
+echo '<script type="module" src="how-2-js.js"></script>' > index.html
+
+# Finally let's create a simple web server
+&>/dev/null python3 -m http.server &
+
+# Now open your browser at the specified port
+xdg-open 'http://localhost:8000'
+```
+
+> `xdg-open` find your default application for the given argument
+> on mac it's just `open` and it's `start` on windows
+
+You can now open your web browser console (`ctrl`+`shift`+`i`)
+and you should see your hello world.
+
+> The console is a very handy place to test code and explore how the language
+> works, don't be shy and play in it !
+
+Great ! you are all set, if you want to re-execute your script, just refresh.
+
+You now just have to create a repository named `piscine-js`,
+which will hold all your solutions for this piscine
+and just add your 2 generated files to it, we will start slow for now... 🐢