Example code comparing different syntax formats of vue3

// Parent component <template>
  <div>
    <div>
      <div>{{city}}</div>
      <button @click="changeReactive">Change reactive</button>
      <button @click="handleFather">Click the parent component</button>
    </div>
    <Child ref="childRef" @handleBtn="handleBtn" @testClick="testClick" city="Chengdu" />
  </div>
</template>

<script>
import { ref, onMounted, toRefs, reactive } from 'vue'
import Child from './Child.vue'

export default {
  components:
    Child
  },
  setup () {
    const handleBtn = (val) => {
      console.log('btn', val)
    }

    const testClick = (val) => {
      console.log('testClick', val)
    }

    const childRef = ref(null)

    const handleFather = () => {
      childRef.value.observed.a = 666 //The parent component modifies the value of the child component console.log('Method for getting the child component', childRef.value)
      // The subcomponent needs to define expose. If not, it needs to be returned. The corresponding function is generally not returned directly. If it is not used on the page, // just expose the required method or value. }

    //Write through the setup function method, need to return, the method used on the page, and the value //If it is a value defined by reactve, the value rendered on the page through deconstruction is not responsive, need to be converted through toRefs, and then deconstructed // ...toRefs(testReactive)
    
    const testReactive = reactive({
      city: 'Beijing',
      age: 22
    })

    const changeReactive = () => {
      testReactive.city = 'Chongqing'
    }

    return {
      handleBtn,
      testClick,
      handleFather,
      ...toRefs(testReactive),
      changeReactive,
      childRef
    }
  }
}
</script>


//Subcomponent <template>
  <div>
    {{observed.a}}
    <button @click="handleBtn">Click</button>
  </div>
</template>

<script>
import { defineProps, defineEmits, defineEmit, defineExpose, reactive } from 'vue'

export default {
  props: {
    city: String
  },

  /* This is mainly set to prevent ctx.attrs from accessing this attribute*/
  /* Some properties set in props will not be displayed in attrs*/

  emits: ['testClick'], //The purpose of setting this is to make sure there is no corresponding custom method on attrs.
  //If peops is set for a subcomponent, the corresponding value cannot be accessed on attrs //arrts has enhanced functionality in vue3, with custom methods, classes, and styles mounted
  //In vue2, the custom method is mounted to $listeners. In vue3, $listeners has been removed. setup (props, ctx) {
    const { expose, emit } = ctx
    const handleBtn = () => {
      console.log('btn', ctx)
      emit('testClick', 666)
    }

    const observed = reactive({
      a: 1
    })

    function clickChild (value) {
      observed.a = value
    }

    expose({
      clickChild, //Expose custom methods, parent component calls observed//Expose the value of the child component})

    return {
      observed,
      handleBtn
    }
  }
}
</script>

// Parent component <template>
  <div>
    <button @click="handleFather">Click on the father</button>
    <Child ref="childRef" @handleBtn="handleBtn" @testClick="testClick" city="Chengdu" />
  </div>
</template>

<script setup>
import { ref } from 'vue'
import Child from './Child.vue'
// This way of writing methods and values ​​that are not used on the return export page, what you need to use is to directly deconstruct the corresponding definition on Vue
const childRef = ref(null)

const handleBtn = (val) => {
  console.log('btn', val)
}

const testClick = (val) => {
  console.log('testClick', val)
}

const handleFather = () => {
  console.log('Method for getting child components', childRef.value)
  childRef.value.testFatherClick() //The parent component calls the method of the child component // The child component exposes the corresponding method through defineExpose}

</script>


// Subcomponent <template>
  <div>
    <button @click="handleBtn">Click</button>
  </div>
</template>

<script setup>
import { defineProps, defineEmits, defineExpose, reactive } from 'vue'

const props = defineProps({
  city: String
})

const emit = defineEmits(['handleBtn', 'testClick'])

const handleBtn = () => {
  // console.log('btn', props, emit)
  emit('testClick', 12)
}

const testFatherClick = () => {
  console.log('Test parent component clicks child component')
}

const observed = reactive({
  a: 1
})

defineExpose({ //Expose method to the parent group testFatherClick,
  observed
})

</script>

<style scoped>
</style>

// Parent component import { ref, reactive } from 'vue'
import Child from './Child.jsx'

const Father = {
  setup() {
    // The ref defined in jsx needs to be accessed through .value when used on the page const city = ref('北京')

    const changeCity = () => {
      city.value = 'Hangzhou'
    }

    const childRef = ref(null)

    const handelFather = (add) => {
      //Also by exposing the expose method in the component // city.value = 'Hangzhou'
      console.log('childRef', childRef.value)
    }

    const testChildClick = (val) => {
      console.log('Test subcomponent click', val)
    }

    return () => {
      return (
        <div>
          <div>{city.value}</div>
          <button onClick={changeCity}>Change city</button>
          <button onClick={handelFather}>Click on the parent</button>
          <Child testChildClick={testChildClick} ref={childRef} />
        </div>
      )
    }
  }
}

export default Father


//Subcomponent import { ref, reactive } from 'vue'

const Child = {
  props: {
    testChildClick: Function
  },

  setup(props, { emit, expose }) {
    const { testChildClick } = props
    const testFatherClick = () => {
      console.log('Test parent component clicks child component')
    }

    const handelBtn = () => {
      // emit('testChildClick') // This doesn't work in jsx // console.log('props', props)
      testChildClick('return value to parent component')
      // This method is the only way to pass a function to the child component, which passes the value to the parent component through the function.}

    expose({
      testFatherClick
    })

    return () => {
      return (
        <div>
          <button onClick={handelBtn}>The child component passes the value to the parent component</button>
        </div>
      )
    }
  }
}

export default Child