Vue advanced (unitary 30): new features of vue3

No Silver Bullet 2020-11-13 07:29:05
vue advanced unitary new features


upgrade Vue 3.0 project

Currently created Vue 3.0 The project needs to go through Plug-in upgrade The way to achieve ,

vue-cli There is no direct support for creating Vue3.0 project , First we go to the project directory , And enter the following command :

cd vue-next-test
vue add vue-next

setup

setup() The function is vue3 Technical secondary school provides new properties for components . It's for us to use vue3 Of Composition API New features provide a unified entry point .

setup The function will be in the beforeCreate after 、created Before that

1.setup Is a new component option , It's something else API Entrance . in other words , All your operations will be in setup Functions are defined and executed internally , Vue3.0 It will also be replaced by a function Vue2.x That is to say new Vue()
2.setup The first parameter is props, there props and Vue2.x Medium props Agreement .
3. When to call ?setup When a component instance is created , Initialize the props Then call , In fact, it replaced Vue2.x Of careted and beforeCreate.
4.setup Return an object , The properties in the object will be directly exposed to the context of the template rendering . And in the Vue2.x in , All attributes you define will be Vue Internal unconditionally exposed to template rendering context .

receive prop

 props: {
p1: String,
},
setup(props, context) {
console.log(props.p1);
},

context

setup The second formal parameter of the function is a context object , This context object contains some useful properties , These attributes are in vue 2.x We need to go through this To access , stay vue 3.x in , They are accessed as follows :

const MyComponent = {
setup(props, context) {
context.attrs
context.slots
context.parent
context.root
context.emit
context.refs
}
}

computed

The behavior of calculated values and calculated properties (computed property) equally : It will only be recalculated if it depends on change . Type A act Of useCallback useMemo.

computed() Returned is a wrapper object , It can be used in the same way as ordinary packaging objects setup() Be returned , It will also be automatically expanded in the rendering context .

Use a :

 setup() {
const num = ref(0);
const get_num = computed(() => num.value + " Compute properties ");
return {
num,
get_num,
};
},

Use two :

// Create a ref Responsive data
const count = ref(1)
// Create a computed Compute properties
const plusOne = computed({
// Value function
get: () => count.value + 1,
// The mutator
set: val => {
count.value = val - 1
}
})
// The operation of assigning values to calculated properties , Will trigger set function
plusOne.value = 9
// Trigger set After the function ,count The value of will be updated
console.log(count.value) // Output 8

Computing properties and data listening

import { ref, computed, watch, watchEffect } from "vue";
export default {
setup() {
const count = ref(0);
const doubleCount = computed(() => {
return count.value * 5;
});
watch(
() => count.value,
(val, oldVal) => {
console.log(`count is ${val}`);
},
{
// Whether to monitor in depth
deep: true,
// Whether to execute it once or not
immediate: true
}
);
function add() {
count.value++;
}
return {
count,
add,
doubleCount
};
}
};

Compute properties computed It's a method , It needs to contain a callback function , When we access the computed property and return the result , Will automatically get the value of the callback function .

Monitor watch It's the same way , It contains 3 Parameters , The first two parameters are function, The third parameter is whether to monitor in depth .

The first parameter is the listening value ,count.value Said when count.value Changes will trigger the listener's callback function , That's the second parameter , The second parameter can execute the callback when listening .

If it is 2 More than listening properties ,

 watch(
[() => count.value, () => name.value],
// Receive two parameters , The first is the new value in the array , The second is that the old values are also in the array
([count, name], [oldCount, oldName]) => {
console.log(count, name);
console.log(oldCount, oldName);
if (count != oldCount) {
console.log("count Voice changes ");
}
if (name != oldName) {
console.log("name Voice changes ");
}
}
);

Get route

 // Get the current component instance
const vue = getCurrentInstance();
// Get the current context
const { ctx } = getCurrentInstance();
// Get route information
console.log(ctx.$router);
function changeRouter() {
// Routing jump
ctx.$router.push("/about");
}

Life cycle

2.x Life cycle options and Composition API Mapping between

  • beforeCreate -> Use setup()

  • created -> Use setup()

  • beforeMount -> onBeforeMount

  • mounted -> onMounted

  • beforeUpdate -> onBeforeUpdate

  • updated -> onUpdated

  • beforeDestroy -> onBeforeUnmount

  • destroyed -> onUnmounted

  • errorCaptured -> onErrorCaptured

Vuex Easy to use

import Vuex from 'vuex'
export default Vuex.createStore({
state: {
num: 1,
},
mutations: {
add(state, value) {
console.log(value)
state.num++
},
decrement(state, value) {
console.log(value)
state.num--
}
},
actions: {
},
modules: {
}
});

Mount to Vue in

import router from './router'
import store from './store'
createApp(App).use(router).use(store).mount('#app')

Components use :

<template>
<div class="home">
<h1>VUEX Use </h1>
<div> Original value :{
{num}}</div>
<div>
<button @click="add"> increase </button>
<button @click="decrement"> Reduce </button>
</div>
</div>
</template>
<script>
import { computed } from "vue";
import { useStore } from "vuex";
export default {
setup() {
const store = useStore();
const num = computed(() => store.state.num);
function add() {
store.commit("add", " increase ");
store.dispatch('action', payload)
}
function decrement() {
store.commit("decrement", " Reduce ");
}
return { num, add, decrement };
}
};
</script>
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