Vue.js 3.0 Tutorial

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Vue 3.0 Style Guide

Vue 3.0 filters

In Vue 3, filters are removed and are no longer part of the official API. Filters were a way to apply common text formatting in Vue 2, but you can easily replace them with methods, computed properties or even a plugin if needed.

Here's how you can replace filters with methods and computed properties:

Methods

Methods are a good replacement for filters that take arguments:

<template>
  <div>{{ formatName(user) }}</div>
</template>

<script>
export default {
  data() {
    return {
      user: {
        firstName: 'John',
        lastName: 'Doe'
      }
    }
  },
  methods: {
    formatName(user) {
      return `${user.lastName}, ${user.firstName}`
    }
  }
}
</script>

Computed Properties

Computed properties are the way to go for more complex formatting that depends on reactive data:

<template>
  <div>{{ fullName }}</div>
</template>

<script>
import { ref, computed } from 'vue';

export default {
  setup() {
    const user = ref({
      firstName: 'John',
      lastName: 'Doe'
    });
    
    const fullName = computed(() => `${user.value.lastName}, ${user.value.firstName}`);
    
    return {
      fullName
    }
  }
}
</script>

Global Filters Replacement

In Vue 2, you could define global filters that would be available in all components. You can achieve similar functionality in Vue 3 by creating a global mixin and defining methods in it:

import { createApp } from 'vue';
import App from './App.vue';

const app = createApp(App);

app.mixin({
  methods: {
    formatCurrency(value) {
      return new Intl.NumberFormat('en-US', { style: 'currency', currency: 'USD' }).format(value);
    }
  }
});

app.mount('#app');

Then in any component:

<template>
  <div>{{ formatCurrency(price) }}</div>
</template>

<script>
export default {
  data() {
    return {
      price: 100
    }
  }
}
</script>

In general, the removal of filters in Vue 3 simplifies the API and encourages the use of methods and computed properties, which are just as powerful and flexible.

Vue 3.0 Built-in Filters: Vue 3.0 has a set of built-in filters for common tasks like formatting dates, currency, and more. For instance, uppercase, lowercase, capitalize, currency, and date are some examples.
```

{{ message | uppercase }}
```

Creating Custom Filters: You can create custom filters using app.directive in the setup function.

// Example custom filter to reverse a string
app.directive('reverse', {
  mounted(el, binding) {
    el.textContent = binding.value.split('').reverse().join('');
  },
});

<!-- Using the custom filter -->
<p v-reverse>{{ message }}</p>

Applying Filters in Vue 3.0 Templates: Filters can be applied directly in templates using the | syntax.
```

{{ dateValue | date('YYYY-MM-DD') }}
```

Vue 3.0 Filter Arguments: Filters can accept arguments for customization.

<!-- Using a filter with arguments -->
<p>{{ price | currency('USD', 2) }}</p>

Chaining Filters: Filters can be chained to perform multiple transformations.
```

{{ message | uppercase | reverse }}
```
Vue 3.0 Filter Usage in Computed Properties: Filters can be used in computed properties for dynamic transformations.
```
computed: {
  formattedMessage() {
    return this.message | uppercase | reverse;
  },
},
```

Vue 3.0 Dynamic Filters: You can dynamically apply filters based on conditions.

<!-- Dynamic filter -->
<p v-if="isUppercase">{{ message | uppercase }}</p>
<p v-else>{{ message | lowercase }}</p>

Vue 3.0 Global Filters: Global filters can be defined and used across components.

app.config.globalProperties.$filters = {
  reverse(value) {
    return value.split('').reverse().join('');
  },
};

<!-- Using a global filter -->
<p>{{ message | $filters.reverse }}</p>

Using Filters with v-bind: Filters can be used with v-bind for dynamic attribute values.
```
<img :src="imagePath | addBaseUrl" alt="Product Image">
```

Updating Filters with Reactivity: Ensure reactivity by using reactive properties within filters.

computed: {
  reversedMessage() {
    return this.message.split('').reverse().join('');
  },
},

<p>{{ reversedMessage }}</p>