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Vue 3 and the Composition API

Vue 2

Vue is Options based

new Vue({
  data: {
    loading: false,
    count: 0,
    user: {}
  },
  computed: {
    double () { return this.count * 2 },
    fullname () {/* ... */}
  },
  methods: {
    increment () { this.count++ },
    fetchUser () {/* ... */}
  }
})

Vue 3

🧱 Composition API

🆕 advanced feature

🚑 options API is not being deprecated

➕ addition to the current API

🧱 Composition API

a set of lower level APIs

use Vue features outside of Vue components

🧱 Composition API

import {ref, computed, watch} from 'vue'

LIVE EXAMPLE

https://stackblitz.com/edit/vitejs-vite-8u3cb5?file=src%2Fmain.js&terminal=dev

New Feature in

Vue 3

the setup option

🧱 Composition API

INSIDE

Vue Components

using setup

new Vue({
  beforeCreate () {

  },
  setup () {
    
  },
  created () {
	
  }
})

the setup option

looks like

Lifecycle hooks

Is More Powerful Than

the setup option

<template>
  <button @click="increaseCount">count {{count}} | double {{double}}</button>
</template>

<script>
  import {computed, ref} from 'vue'
  export default {
    setup () {
      const count = ref(0)
      const double = computed(() => count.value * 2)
      const increaseCount = () => {
        count.value++
      }
      return {increaseCount, count, double} // render context - unwrapped
    },
    mounted () {
      this.count = 40
      this.increaseCount()
    }
  }
</script>

the setup option

ButtonCounter.vue

Questions?

Exercise 1

@danielkelly_io

@danielkellyio

Alabama, USA

Daniel Kelly

Teacher @ Vue School

Full Stack developer (10 years)

Husband and Father

setup(){
  //...
  return { 
    characters, 
    loadingState, 
    fetchAllCharacters 
  };
}

Gets Really Annoying

`<script setup>`

compile-time syntactic sugar for using Composition API inside Single-File Components (SFCs)

<script setup>
import { ref } from "vue";
const characters = ref([]);
const loadingState = ref(null);
function fetchAllCharacters() {
  //...
}
</script>

<script setup>
 //...
</script>
<template> 
 //...  
</template>

Convention = Script setup ABOVE template

Import Components to Register them

<script>
import HelloWorld from "@/components/HelloWorld.vue";

export default {
  components: {
    HelloWorld,
  },
};
</script>

<script setup>
import HelloWorld from "@/components/HelloWorld.vue";
</script>

Import Components to Register them

<script setup>
// enables v-focus in templates
const vFocus = {
  mounted: (el) => el.focus()
}
</script>

<template>
  <input v-focus />
</template>

Define directives by prefixing with v

Questions?

Exercise 2

Why Composition API

♻️ Logic Reuse

🗂 Code Organization

📐 Improved TypeScript Support

🗂 Code Organisation

Organise Code By Options

  import axios from 'axios'
  import orderBy from 'lodash.orderby'
  export default {
    data () {
      return {
        characters: [],
        loadingState: null,
        orderKey: 'id'
      }
    },
    computed: {
      charactersOrdered() {
        return orderBy(this.characters, this.orderKey)
      }
    },
    methods: {
      fetchAllCharacters () {
        this.loadingState = 'loading'
        axios.get('https://rickandmortyapi.com/api/character')
          .then(response => {
            setTimeout(() => {
              this.loadingState = 'success'
              this.characters = response.data.results
            }, 1000)
          })
      },
      setOrderKey(key) {
        this.orderKey = key
      }
    },
    created () {
      this.fetchAllCharacters()
    }
  }

Fetch Resource Feature

Order Array Feature

<script setup>
import axios from 'axios'
import orderBy from 'lodash/orderby'
import {computed, ref} from 'vue'

const characters = ref([])
const loadingState = ref(null)

const fetchAllCharacters = () => {
  loadingState.value = 'loading'
  return axios.get('https://rickandmortyapi.com/api/character')
    .then(response => {
      loadingState.value = 'success'
      characters.value = response.data.results
    })
}
fetchAllCharacters()

const orderKey = ref('id')
const charactersOrdered = computed(() => {
  return orderBy(characters.value, orderKey.value)
})

const setOrderKey = (key) => {
  orderKey.value = key
}

</script>

Organise Code By Feature

Fetch Resource Feature

Order Array Feature

Code Organisation

By Options VS By Feature

https://vue-composition-api-rfc.netlify.com/#code-organization

Questions?

Exercise 3

♻️ Logic Reuse

Logic Reuse

<template>
  <button @click="increaseCount">count {{count}} | double {{double}}</button>
</template>

<script>
  import {computed, ref} from 'vue'
  export default {
    setup () {
      const count = ref(0)
      const double = computed(() => count.value * 2)
      const increaseCount = () => {
        count.value++
      }
      return {increaseCount, count, double} // render context - unwrapped
    },
    mounted () {
      this.count = 40
      this.increaseCount()
    }
  }
</script>

Button Component From Earlier

<script>
  import {computed, ref} from 'vue'
  const useCounter = () => {
    const count = ref(0)
    const double = computed(() => count.value * 2)
    const increaseCount = () => {
      count.value++
    }

    return {count, double, increaseCount}
  }
  export default {
    setup () {
      const {increaseCount, count, double} = useCounter()
      return {increaseCount, count, double} // render context
    }
  }
</script>

Logic Reuse

<script>
  import {computed, ref} from 'vue'
  const useCounter = (initial = 0) => {
    const count = ref(initial)
    const double = computed(() => count.value * 2)
    const increaseCount = () => {
      count.value++
    }

    return {count, double, increaseCount}
  }
  export default {
    setup () {
      const {increaseCount, count, double} = useCounter(40)
      return {increaseCount, count, double}
    }
  }
</script>

Logic Reuse

// src/composables/useCounter.js
import {computed, ref} from 'vue'
export const useCounter = (initial = 0) => {
  const count = ref(initial)
  const double = computed(() => count.value * 2)
  const increaseCount = () => {
    count.value++
  }

  return {count, double, increaseCount}
}

Logic Reuse

Can extract to another file

// src/composables/useCounter.js
import {computed, ref} from 'vue'
export const useCounter = (initial = 0) => {
  const count = ref(initial)
  const double = computed(() => count.value * 2)
  const increaseCount = () => {
    count.value++
  }

  return {count, double, increaseCount}
}

Logic Reuse

Can extract to another file

// CounterButton.vue
<script>
  import {useCounter} from "@/composables/useCounter"
  export default {
    setup () {
      const {increaseCount, count, double} = useCounter(40)
      return {increaseCount, count, double}
    }
  }
</script>

// src/composables/useCounter.js
import {computed, ref} from 'vue'
export const useCounter = (initial = 0) => {
  const count = ref(initial)
  const double = computed(() => count.value * 2)
  const increaseCount = () => {
    count.value++
  }

  return {count, double, increaseCount}
}

Logic Reuse

Can extract to another file

// CounterButton.vue
<script setup>
  import {useCounter} from "@/composables/useCounter"
  const {increaseCount, count, double} = useCounter(40)
</script>

Logic Reuse

Fetch Data

// /src/composables/useFetchResource.js
import {ref} from 'vue'
import axios from 'axios'

export default function useFetchResource (url) {
  const data = ref([])
  const loadingState = ref(null)

  const fetchResource = () => {
    loadingState.value = 'loading'
    return axios.get(url)
      .then(response => {
        loadingState.value = 'success'
        data.value = response.data.results
      })
  }

  return {data, loadingState, fetchResource}
}

Logic Reuse

Fetch Data

The Component

<script setup>
  // ...
const characters = ref([]);
const loadingState = ref(null);
function fetchAllCharacters() {
  loadingState.value = "loading";
  axios.get("https://rickandmortyapi.com/api/character").then((response) => {
    setTimeout(() => {
      loadingState.value = "success";
      characters.value = response.data.results;
    }, 1000);
  });
}
fetchAllCharacters();
</script>

CharacterCards.vue

The Component

<script setup>
import { useFetchResource } from "@/composables/useFetchResource";
// ...
const {
  data: characters,
  fetchResource: fetchAllCharacters,
  loadingState,
} = useFetchResource("https://rickandmortyapi.com/api/character");
fetchAllCharacters();
</script>

CharacterCards.vue

<template></template>


<script>
  import useMousePosition from '@/composables/useMousePosition'

  export default {
    setup () {
      const {x, y} = useMousePosition()

      // ...
    }
  }
</script>

🐭 Logic Reuse

VueUse

Logic Reuse Alternatives

Mixins
Higher Order Components
Renderless Components

Respective Drawbacks when compared with the Composition API

https://vueschool.io/articles/vuejs-tutorials/what-is-a-vue-js-composable/

Questions?

Exercises 4-5

LifeCycle Hooks

https://vuejs.org/guide/essentials/lifecycle.html#lifecycle-diagram

LifeCycle Hooks

// MyComponent.vue
<script setup>
import { onMounted, onUnmounted } from "vue";
onMounted(()=>{
  // do things
})
</script>

LifeCycle Hooks

// useMyComposable.js
import { onMounted, onUnmounted } from "vue";
export function useMyComposable(){
  
  onMounted(()=>{
    // do things
  })

}

Questions?

Exercise 6

Props In the Composition API

<script>
export default {
  props: ['foo'],
  setup(props) {
    // setup() receives props as the first argument.
    console.log(props.foo)
  }
}
</script>

Props In the Composition API

<script setup>
const props = defineProps({
  foo: String,
});

console.log(props.foo)
</script>

Events In the Composition API

<script>
export default {
  emits: ['inFocus', 'submit'],
  setup(props, ctx) {
    ctx.emit('submit')
  }
}
</script>

Events In the Composition API

<script setup>
const emit = defineEmits([
  'inFocus', 
  'submit'
])

emit('submit')
</script>

Template Refs In the Composition API

<script>
  export default{
    onMounted(){
      this.$refs.input.focus()
    }
  }
</script>

<template>
  <input ref="input" />
</template>

Template Refs In the Composition API

<script setup>
import { ref, onMounted } from 'vue'

// declare a ref to hold the element reference
// the name must match template ref value
const input = ref(null)

onMounted(() => {
  input.value.focus()
})
</script>

<template>
  <input ref="input" />
</template>

The Reactive Function

<script setup>
const framework = reactive({
  name: 'Vue',
  author:'Evan You',
  tags: ['javascript', 'vue']
})

framework.name // no need for .value
</script>

Alternative way to declare reactive data

Ref vs Reactive

// ✅ ref works
const framwork = ref('Vue')
const isAwesome = ref(true)
const created = ref(2014)

Ref Works on Primitives

Reactive does not

// ❌ won't work 
const framwork = reactive('Vue') 
const isAwesome = reactive(true)
const created = reactive(2014)

// ✅ ref works
let posts = ref(['post 1', 'post 2'])
posts.value = ['post 3', 'post 4']

Can Re-assign whole ref values but not reactive

// ❌ won't work 
let posts = reactive(['post 1', 'post 2'])
posts = ['post 3', 'post 4']

// ref
const framework = ref({
  name: 'Vue',
  author:'Evan You',
  tags: ['javascript', 'vue']
})
                       ⬇️
console.log(framework.value.name)

Ref requires .value reactive does not

// reactive
const framework = reactive({
  name: 'Vue',
  author:'Evan You',
  tags: ['javascript', 'vue']
})

console.log(framework.name)

Which to use? 🤔

Sometimes you have no choice
- Must use refs for primitives
- Must use ref when replacing whole value
Otherwise it's personal preference
Many choose to use ref for everything

// ref
const {name} = toRefs(reactive({
  name: 'Vue',
  author:'Evan You',
  tags: ['javascript', 'vue']
}))

console.log(name.value)

Can convert reactive object to refs

Questions?

Exercises 7-8

Conclusion

Composition API Benefits

extremely flexible
clear source of properties
performance
no namespace collision
new libs written for CAPI

Consider 🙏

no need to rewrite your Vue 2 app
no need to use it in a simple component
keep the junior devs in mind

(own opinion)

Good Fit For

component code grows too long
team that work on the same (big) components
reuse component options without using mixins
when TypeScript support is important
The whole team agrees to do CAPI everywhere

(own opinion)

How was the pace of workshop? 🧐

Too Easy
Too Hard
Just Fine

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Vue 3 and the Composition API (v2)

By Daniel Kelly

Vue 3 and the Composition API (v2)

Vue 3 and the Composition API

1,389