Modularity is when we use one piece of code (module) for all similar parts of our app.
What we have written until now are markup with repeating parts, and styles. E.g. there is a lot of similar blocks for each key (hundreds of them, and can be thousands):
<div class="key">
<div class="main">2</div>
<div class="shifted">@</div>
</div>
Now, if we decide to change something in such elements, we should change them all manually.
If we had only 1 template for each key, changing code in one place will automatically change every key in the app.
JavaScript
I am sorry to say, but: HTML and CSS aren't programming languages.
Modularity can be achieved only by programming.
Browser apps are coded in JavaScript (JS).
JS was made in 1995 and DOM (document object model in the browser) — in 1998. Writing code in plain (vanilla) JS and direct manipulations with DOM is kinda hard (and old-fashioned).
But there is no alternative to JS.
Framework
So programmers invented modern frameworks, that make coding web apps easier, clearer and faster. We will use the simplest of them: Vue. Frameworks also allow us to write JS in a component way. Component is a module with a template and all its logic.
Setup
In index.html comment all code inside tag <body>. We need later, but not now.
index.html
<body>
<!--
...
-->
</body>
Copy code example from: https://vuejs.org/guide/quick-start.html#without-build-tools (or from here):
<script src="https://unpkg.com/vue@3"></script>
<div id="app">{{ message }}</div>
<script>
const { createApp } = Vue
createApp({
data() {
return {
message: 'Hello Vue!'
}
}
}).mount('#app')
</script>
and paste it to index.html after <body> tag. Save file and look at the app in the browser. If “Hello Vue!” appeared on top of the page it means that setup works.
Even though it works, we need to organize code better.
Entry point — index.js
Put first <script> tag into the <head> tag.
index.html
<head>
...
<script src="https://unpkg.com/vue@3"></script>
</head>
Cut second <script> tag content (ctrl+x) and remove remained wrapper. Create in the project root directory a file index.js and paste there what you've copied before.
index.js
const { createApp } = Vue
createApp({
data() {
return {
message: 'Hello Vue!'
}
}
}).mount('#app')
In index.html, add string just before closing </body> tag:
index.html
...
<script src="./index.js" type="module"></script>
</body>
Attribute type="module" allows us to use ES6 feature import/export. We need it on the next step.
index.html (result)
<head>
...
<script src="https://unpkg.com/vue@3"></script>
</head>
<body>
<div id="app">{{ message }}</div>
<!-- ... -->
<script src="./index.js" type="module"></script>
</body>
If you did everything right, you should see "Hello Vue!" at the top of the page as before.
index.js is called the entry point. It mounts all our app code into index.html document.
We put <script src="https://unpkg.com/vue@3"> on the top of the document because we need to load framework code as soon as possible.
And we put the <script src="./index.js" type="module"> on the bottom, because written by us code needs everything above loaded before it can work.
Root component — App.js
Open index.js. The code inside createApp(...) is a vue component called the root component — cut it (ctrl+x or copy and delete). We will move it to separate file. Create in the project root directory a file App.js. Paste there a code you copied before (ctrl+v) to const App. Then export it.
App.js
const App = {
data() {
return {
message: 'Hello Vue!!'
}
}
}
export default App
Then import it in index.js and put into createApp(...)
index.js
import App from './App.js'
const { createApp } = Vue
createApp(App).mount('#app')
If you did everything right, you should see "Hello Vue!" in the browser as before.
Components hierarchy
First we create all components as colored rectangles to test how works our framework, and to build component hierarchy:
<App>
<LangSwitcher />
<Keyboard>
<Key />
</Keyboard>
</App>
<App> is parent for <LangSwitcher> and <Keyboard>.
<Keyboard> is parent for <Key>.
<App> is grandpa for <Key>.
We can also say, that <Key> is a child of <Keyboard> etc.
App
We already have App component. Just add to
styles.css
...
#app {
background-color: red;
padding: 10px;
}
All styles in this section are temporary, we need them to see component nesting. Then we'll delete them.
Now App is a red rectangle.
LangSwitcher
Create a directory components in the project root directory, and create there a file LangSwitcher.js
const LangSwitcher = {
template: `<div class="langSwitcher">LangSwitcher</div>`
}
export default LangSwitcher
Vue component is a JS object with predefined properties. One of them is template. We assigned to property template a string value with a plain html.
Write styles for it.
styles.css
.langSwitcher {
background-color: green;
padding: 10px;
}
Add a newly created component to the root component
App.js
import LangSwitcher from './components/LangSwitcher.js'
const App = {
template: `App <vue-lang-switcher />`,
components: {
'vue-lang-switcher': LangSwitcher
}
}
export default App
If we use one component inside another, we should fill components property with an object. A property 'vue-lang-switcher' is a valid custom html tag name. Its value is imported LangSwitcher module. After that we can use imported (child) component inside template.
Result:
We see here that App contains LangSwitcher which is correct.
Keyboard
Create a file Keyboard.js in the components folder
Keyboard.js
const Keyboard = {
template: `<div class="keyboard">Keyboard</div>`
}
export default Keyboard
Add to
styles.css
.keyboard {
background-color: blue;
padding: 10px;
display: flex; /* to display keys in a row, on the next step */
}
Add a new component Keyboard to
App.js
import LangSwitcher from './components/LangSwitcher.js'
import Keyboard from './components/Keyboard.js'
const App = {
template: `App
<vue-lang-switcher />
<vue-keyboard />
`,
components: {
'vue-lang-switcher': LangSwitcher,
'vue-keyboard': Keyboard
}
}
export default App
Now the app looks like:
Key
Create file Key.js in components directory
Key.js
const Key = {
template: `<div class="key">Key</div>`
}
export default Key
Add to
styles.css
.key {
background-color: yellow;
padding: 10px;
color: black;
}
As you remember Key is the child of Keyboard, so it should be imported in Keyboard, not in App.js.
Keyboard.js
import Key from './Key.js'
const Keyboard = {
template: `<div class="keyboard">
Keyboard
<vue-key />
<vue-key />
<vue-key />
</div>`,
components: {
'vue-key': Key
}
}
export default Keyboard
Save all files.
Result
Our component hierarchy works well. All components have correct nesting. How we said it the beginning of the chapter:
<App>is parent for<LangSwitcher>and<Keyboard>.
<Keyboard>is parent for<Key>.
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