7. Interactivity 1. Switching keyboards

• Reactive state, @click event, method call (refactor LangSwitcher)
• Conditional styling
• Change parent state from a child
• Switching keyboards (languages)
  • Another languages data
  • Dynamic import for keyboardData

Interactivity is when a user interacts with an app, and see results (almost immediately).

Our app should handle user generated events: mouse clicks, phone screen taps, keyboard key presses.

Reactive state, @click event, method call (refactor LangSwitcher)

When we change a component variable value (state), and it causes change in a visible app (view), it is called reactive state. Reactivity means connection between component variables and a view.

• In vue such reactive variables should be placed in the method data().
• The most common approach to change them — by methods.
• Methods are called from event listeners, described in methods, and placed in a template (e.g. @click="keyClick(keyContent)").

Let’s add to LangSwitcher:

• a method data() with a returned property (state) currentLang: 'en' (‘en’ as default)
• a property methods with a new method switchLang(lang)
• in the template
  • a new event handler @click to element <div class="lang">
  • a new div to display reactive variable currentLang. It is temporary, after testing we’ll delete it.

The idea is to move the red circle to the lang code that we clicked. Also, we need to store selected lang in some variable.

LangSwitcher.js

const LangSwitcher = {
    template: `
    <div class="langSwitcher">
        <div 
            v-for="lang in langs" 
            class="lang"
            @click="switchLang(lang)"
        >
            {{lang}}
        </div>
    </div>
    <div style="text-align: center;">
        {{currentLang}}
    </div>`,
    props: {
        langs: Array
    },
    /* add: */
    data() {
        return {
            currentLang: 'en'
        }
    },
    /* add: */
    methods: {
        switchLang(lang) {
            this.currentLang = lang
        }
    }
}

export default LangSwitcher

In the template @click="switchLang(lang)" -- by clicking on the element where it placed (<div class=”lang”>) the method switchLang will be called with a parameter lang wich is particular to each <div> and can be ‘en’, ‘ru’, ‘ar’.

That’s how a user input (click) on dynamic generated elements changes a reactive state.

Result:

You see that after a click on a lang code, component state currentLang is changed in the div below.

Conditional styling

Instead of the currentLang text, we need a red round background under the active lang.

Conditional styling is when we apply some styling to an element, only if a condition is true.

:class='["lang", {active: currentLang === lang}]' this string in a template will do all work for us.

LangSwitcher.js template

<div
    v-for="lang in langs"
    :class='["lang", {active: currentLang === lang}]'
    @click="switchLang(lang)"
>
    {{lang}}
</div>

1-st element in the array is a string (because of quotes), that means that the class lang will be attached to <div> in any case (without condition).

2-nd element is an object like {styleName: booleanCondition}. Class active will be attached to <div class="lang"> only if the prop lang of the element is equal to the state currentLang.

In styles.css we defined before:

.lang {
    width: 2rem;
    height: 2rem;
    border-radius: 1rem;
    ...;
}

.langSwitcher .active {
    background-color: red;
    color: white;
}

That’s why the red round follows our clicks on lang codes — because of attaching and detaching the class active.

Result:

Diffs in code 7.1

Change parent state from a child

Changing parent state from a child is kinda opposite to passing props from parent to child (what we made a lot before). It is another important approach to share data between components

• In a parent we create a reactive state and a method to change it
• we pass this method to child as a prop
• we call it (with params) from the child

When you call a method received from a prop, notice that actually it happens where it was defined, not where it was called from.

If the parent state was passed as a prop to multiple components, if we change this state (from any child, by method received as a prop) — then all components with this state (as prop) will be updated. That is how a little child component from hierarchy bottom can globally affect on the whole app — by calling a method, that changes parent state.

In small apps like our, it is common to have reactive state and main logic in the top level component as <App> and pass the state and methods to children (<Keyboard>, <LangSwitcher>) as props.

For now currentLang is placed in <LangSwitcher>. But we need this value also in <Keyboard> and <Key>.

<LangSwitcher> and <Keyboard> are siblings, they haven’t parent-child relations, but have common parent. So, to share the state currentLang between siblings, we should lift it up to the common ancestor <App>.

(image from chapter 4)

Let’s move state currentLang and method switchLang from <LangSwitcher> to <App> and then pass them as props to <LangSwitcher> and use them there.

Open LangSwitcher.js and remove data() and methods. Add to props: currentLang, switchLang.

LangSwitcher.js

const LangSwitcher = {
    template: `
    <div class="langSwitcher">
        <div 
            v-for="lang in langs" 
            :class='["lang", {active: currentLang === lang}]'
            @click="switchLang(lang)"
        >
            {{lang}}
        </div>
    </div>`,
    props: {
        langs: Array,
        /* add: */
        currentLang: String,
        switchLang: Function
    }
    /* delete: 
    data() {
        return {
            currentLang: 'en'
        }
    },
    methods: {
        switchLang(lang) {
            this.currentLang = lang
        }
    } 
    */
}

export default LangSwitcher

Open App.js. Add to data() a new state currentLang: 'en'. Paste whole methods from old LangSwitcher.js.

In the template

• pass to <vue-lang-switcher> 2 new props: switchLang and currentLang
• add {{currentLang}} to test our changes.

App.js

import Keyboard from './components/Keyboard.js'
import LangSwitcher from './components/LangSwitcher.js'

const App = {
    template: `App-{{currentLang}}
    <vue-lang-switcher 
        :langs="langs" 
        :switchLang="switchLang" 
        :currentLang="currentLang" 
    />
    <vue-keyboard />
    `,
    components: {
        'vue-lang-switcher': LangSwitcher,
        'vue-keyboard': Keyboard
    },
    mounted() {
        import(`./keyboardData/en.js`).then(result => {
            const { default: keyboardData } = result
            this.keyboardData = keyboardData
        })
    },
    data() {
        return {
            langs: ['en', 'ru', 'ar'],
            /* add: */
            currentLang: 'en'
        }
    },
    /* add: */
    methods: {
        switchLang(lang) {
            this.currentLang = lang
        }
    }
}

export default App

Result:

Notice, when we do something in LangSwitcher it changes App state. We change the parent state from the child with the method that we passed from the parent to the child as a prop. Before these changes currentLang was available only in <LangSwitcher>, and <App> hasn't access to it. Now <App> and <LangSwitcher> have access to currentLang. And we can pass it also to <Keyboard> and <Key>.

Diffs in code 7.2

Switching keyboards (languages)

Another languages data

Open a folder keyboardData. Copy and paste there a file en.js twice. Rename clones to ru.js and ar.js. Change a content (copy from here or type).

ru.js

const keyboard = [
    [
        { code: 'Escape', label: 'Esc' },
        { code: 'F1' },
        { code: 'F2' },
        { code: 'F3' },
        { code: 'F4' },
        { code: 'F5' },
        { code: 'F6' }
    ],
    [
        {
            code: 'Backquote',
            main: 'ё',
            shifted: 'Ё'
        },
        {
            code: 'Digit1',
            main: '1',
            shifted: '!'
        },
        {
            code: 'Digit2',
            main: '2',
            shifted: '"'
        },
        {
            code: 'Digit3',
            main: '3',
            shifted: '№'
        },
        {
            code: 'Digit4',
            main: '4',
            shifted: ';'
        },
        {
            code: 'Digit5',
            main: '5',
            shifted: '%'
        }
    ],
    [
        { code: 'Tab' },
        {
            code: 'KeyQ',
            main: 'й',
            shifted: 'Й'
        },
        {
            code: 'KeyW',
            main: 'ц',
            shifted: 'Ц'
        },
        {
            code: 'KeyE',
            main: 'у',
            shifted: 'У'
        },
        {
            code: 'KeyR',
            main: 'к',
            shifted: 'К'
        }
    ]
]

export default keyboard

ar.js

const keyboard = [
    [
        { code: 'Escape', label: 'Esc' },
        { code: 'F1' },
        { code: 'F2' },
        { code: 'F3' },
        { code: 'F4' },
        { code: 'F5' },
        { code: 'F6' }
    ],
    [
        {
            code: 'Backquote',
            main: '٫',
            shifted: '٬'
        },
        {
            code: 'Digit1',
            main: '١',
            shifted: '!'
        },
        {
            code: 'Digit2',
            main: '٢',
            shifted: '@'
        },
        {
            code: 'Digit3',
            main: '٣',
            shifted: '#'
        },
        {
            code: 'Digit4',
            main: '٤',
            shifted: '$'
        },
        {
            code: 'Digit5',
            main: '٥',
            shifted: '٪'
        }
    ],
    [
        { code: 'Tab' },
        {
            code: 'KeyQ',
            main: 'ض',
            shifted: 'َ'
        },
        {
            code: 'KeyW',
            main: 'ص',
            shifted: 'ً'
        },
        {
            code: 'KeyE',
            main: 'ث',
            shifted: 'ُ'
        },
        {
            code: 'KeyR',
            main: 'ق',
            shifted: 'ٌ'
        }
    ]
]

export default keyboard

Arabic diacritic symbols aren't looking good in the code. But don't worry about it. It will work well for our purposes.

Dynamic import for keyboardData

In App.js pass currentLang to Keyboard.

App.js template

<vue-keyboard :currentLang="currentLang" />

In Keyboard.js:

• receive the new prop
• watch its changes
• add a new method getKeyboardData
• call getKeyboardData on mounted() and on change prop currentLang

Keyboard.js

import Key from './Key.js'

const Keyboard = {
    template: `
    <div class="keyboard">
        <div
            v-for="(row, index) in keyboardData"
            :class="['row', 'row-'+(index+1)]"
        >
            <vue-key
                v-for="keyContent in row"
                :keyContent="keyContent"
            />
        </div>
    </div>
`,
    components: {
        'vue-key': Key
    },
    data() {
        return { keyboardData: [] }
    },
    /* receive a new prop  */
    props: {
        currentLang: String
    },
    watch: {
        /* add function, that will be called when prop changes */
        currentLang: function (currentLang) {
            this.getKeyboardData(currentLang)
        }
    },
    /* happens when app opened for the first time */
    mounted() {
        this.getKeyboardData(this.currentLang)
    },
    methods: {
        async getKeyboardData(lang) {
            const { default: keyboardData } = await import(
                `../keyboardData/${lang}.js`
            )
            this.keyboardData = keyboardData
        }
    }
}

export default Keyboard

If you noticed async/await in the method getKeyboardData -- that is an alternative syntax for promises. This code is asynchronous, because reading a file takes time, and we should wait for result to move further through our scenario.

Result:

We shared currentLang state between siblings LangSwitcher and Keyboard through their common ancestor App.

With a few lines of code we achieved a big improvement of functionality. That is because we organized code well: in a modular way, with intuitive props, methods, and structure.

Diffs in code 7.3

Entire code after the chapter