128 lines
3.4 KiB
Markdown
128 lines
3.4 KiB
Markdown
# Migration to Vue 3
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In order to prepare for the eventual migration to Vue 3.x, we should be wary about adding the following features to the codebase:
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## Vue filters
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**Why?**
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Filters [are removed](https://github.com/vuejs/rfcs/blob/master/active-rfcs/0015-remove-filters.md) from the Vue 3 API completely.
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**What to use instead**
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Component's computed properties / methods or external helpers.
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## Event hub
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**Why?**
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`$on`, `$once`, and `$off` methods [are removed](https://github.com/vuejs/rfcs/blob/master/active-rfcs/0020-events-api-change.md) from the Vue instance, so in Vue 3 it can't be used to create an event hub.
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**What to use instead**
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Vue docs recommend using [mitt](https://github.com/developit/mitt) library. It's relatively small (200 bytes gzipped) and has a simple API:
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```javascript
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import mitt from 'mitt'
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const emitter = mitt()
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// listen to an event
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emitter.on('foo', e => console.log('foo', e) )
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// listen to all events
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emitter.on('*', (type, e) => console.log(type, e) )
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// fire an event
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emitter.emit('foo', { a: 'b' })
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// working with handler references:
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function onFoo() {}
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emitter.on('foo', onFoo) // listen
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emitter.off('foo', onFoo) // unlisten
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```
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**Event hub factory**
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To make it easier for you to migrate existing event hubs to the new recommended approach, or simply
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to create new ones, we have created a factory that you can use to instantiate a new mitt-based
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event hub.
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```javascript
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import createEventHub from '~/helpers/event_hub_factory';
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export default createEventHub();
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```
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Event hubs created with the factory expose the same methods as Vue 2 event hubs (`$on`, `$once`, `$off` and
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`$emit`), making them backward compatible with our previous approach.
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## \<template functional>
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**Why?**
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In Vue 3, `{ functional: true }` option [is removed](https://github.com/vuejs/rfcs/blob/functional-async-api-change/active-rfcs/0007-functional-async-api-change.md) and `<template functional>` is no longer supported.
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**What to use instead**
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Functional components must be written as plain functions:
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```javascript
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import { h } from 'vue'
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const FunctionalComp = (props, slots) => {
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return h('div', `Hello! ${props.name}`)
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}
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```
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NOTE: **Note:**
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It is not recommended to replace stateful components with functional components unless you absolutely need a performance improvement right now. In Vue 3, performance gains for functional components will be negligible.
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## Old slots syntax with `slot` attribute
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**Why?**
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In Vue 2.6 `slot` attribute was already deprecated in favor of `v-slot` directive but its usage is still allowed and sometimes we prefer using them because it simplifies unit tests (with old syntax, slots are rendered on `shallowMount`). However, in Vue 3 we can't use old syntax anymore.
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**What to use instead**
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The syntax with `v-slot` directive. To fix rendering slots in `shallowMount`, we need to stub a child component with slots explicitly.
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```html
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<!-- MyAwesomeComponent.vue -->
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<script>
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import SomeChildComponent from './some_child_component.vue'
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export default {
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components: {
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SomeChildComponent
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}
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}
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</script>
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<template>
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<div>
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<h1>Hello GitLab!</h1>
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<some-child-component>
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<template #header>
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Header content
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</template>
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</some-child-component>
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</div>
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</template>
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```
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```javascript
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// MyAwesomeComponent.spec.js
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import SomeChildComponent from '~/some_child_component.vue'
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shallowMount(MyAwesomeComponent, {
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stubs: {
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SomeChildComponent
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}
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})
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```
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