Commit e650197f authored by Natalia Tepluhina's avatar Natalia Tepluhina Committed by Phil Hughes

Added Vue 3 migration doc to Frontend development guidelines

parent bc5cf0b7
...@@ -289,3 +289,16 @@ One should apply to be a Vue.js expert by opening an MR when the Merge Request's ...@@ -289,3 +289,16 @@ One should apply to be a Vue.js expert by opening an MR when the Merge Request's
- Full understanding of testing a Vue and Vuex application - Full understanding of testing a Vue and Vuex application
- Vuex code follows the [documented pattern](vuex.md#actions-pattern-request-and-receive-namespaces) - Vuex code follows the [documented pattern](vuex.md#actions-pattern-request-and-receive-namespaces)
- Knowledge about the existing Vue and Vuex applications and existing reusable components - Knowledge about the existing Vue and Vuex applications and existing reusable components
## Vue 2 -> Vue 3 Migration
> This section is added temporarily to support the efforts to migrate the codebase from Vue 2.x to Vue 3.x
Currently, we recommend to minimize adding certain features to the codebase to prevent increasing the tech debt for the eventual migration:
- filters;
- event buses;
- functional templated
- `slot` attributes
You can find more details on [Migration to Vue 3](vue3_migration.md)
# Migration to Vue 3
In order to prepare for the eventual migration to Vue 3.x, we should be wary about adding the following features to the codebase:
## Vue filters
**Why?**
Filters [are removed](https://github.com/vuejs/rfcs/blob/master/active-rfcs/0015-remove-filters.md) from the Vue 3 API completely.
**What to use instead**
Component's computed properties / methods or external helpers.
## Event bus
**Why?**
`$on` and `$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 bus.
**What to use instead**
Vue docs recommend using [mitt](https://github.com/developit/mitt) library. It's relatively small (200 bytes gzipped) and has a simple API:
```javascript
import mitt from 'mitt'
const emitter = mitt()
// listen to an event
emitter.on('foo', e => console.log('foo', e) )
// listen to all events
emitter.on('*', (type, e) => console.log(type, e) )
// fire an event
emitter.emit('foo', { a: 'b' })
// working with handler references:
function onFoo() {}
emitter.on('foo', onFoo) // listen
emitter.off('foo', onFoo) // unlisten
```
## <template functional>
**Why?**
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.
**What to use instead**
Functional components must be written as plain functions:
```javascript
import { h } from 'vue'
const FunctionalComp = (props, slots) => {
return h('div', `Hello! ${props.name}`)
}
```
## Old slots syntax with `slot` attribute
**Why?**
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.
**What to use instead**
The syntax with `v-slot` directive. To fix rendering slots in `shallowMount`, we need to stub a child component with slots explicitly.
```html
<!-- MyAwesomeComponent.vue -->
<script>
import SomeChildComponent from './some_child_component.vue'
export default {
components: {
SomeChildComponent
}
}
</script>
<template>
<div>
<h1>Hello GitLab!</h1>
<some-child-component>
<template #header>
Header content
</template>
</some-child-component>
</div>
</template>
```
```js
// MyAwesomeComponent.spec.js
import SomeChildComponent from '~/some_child_component.vue'
shallowMount(MyAwesomeComponent, {
stubs: {
SomeChildComponent
}
})
```
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