Analysis of basic principles and code examples of Vue3 implementation of two-way binding

In Vue3, two-way binding is throughv-modelThe implementation of the instruction mainly depends onResponsive systemandEvent mechanism. The responsive system in Vue3 isProxyImplementation, it replaces the, providing more powerful features and better performance.

The following is the basic principles and code example analysis of Vue3's implementation of two-way binding:

1. The principle of two-way binding

Data responsiveness:
Vue3 UseProxyHijacking data objects, and when data changes, view updates can be sensed and notified.

Event listening:
v-modelEssentially syntactic sugar, it is equivalent to bindingvalueandinputevent. Component passpropsReceive data (modelValue),passemitTrigger event notify the parent component (update:modelValue）。

2. Code example: implement two-way binding in ordinary components

Parent component code:

<template>
  <div>
    <h1>Vue3 Two-way binding example</h1>
    <!-- usev-modelTwo-way binding -->
    <CustomInput v-model="inputValue" />
    <p>Values ​​in parent component：{{ inputValue }}</p>
  </div>
</template>
<script>
import CustomInput from './';
export default {
  components: { CustomInput },
  data() {
    return {
      inputValue: '' // Parent component's data    };
  }
};
</script>

Subcomponent code:

<template>
  <div>
    <!-- The child component accepts the value passed by the parent component -->
    <input :value="modelValue" @input="onInput" />
  </div>
</template>
<script>
export default {
  props: {
    // Receive the value passed by the parent component    modelValue: {
      type: String,
      required: true
    }
  },
  methods: {
    // Trigger event to pass data back to the parent component    onInput(event) {
      this.$emit('update:modelValue', );
    }
  }
};
</script>

Execution process:

Parent component usagev-model="inputValue"Bind data.

Vue3 willv-model="inputValue"Resolution as:

:modelValue="inputValue" @update:modelValue="value => inputValue = value"

The parent component willinputValueValue passedmodelValuePass to child components.

Subcomponent monitoringinputEvent, when the content of the input box changes,$emit('update:modelValue', newValue)Notify the parent component to update the data.

Parent component updateinputValue, trigger responsive updates, and the view is refreshed synchronously.

3. Analysis of core code of Vue3 responsive system

Vue3's responsive system usageProxyaccomplish. Here is a simplified version of the core principle:

// Define responsive objectsfunction reactive(target) {
  return new Proxy(target, {
    get(target, key, receiver) {
      (`Access properties: ${key}`);
      return (target, key, receiver);
    },
    set(target, key, value, receiver) {
      (`Set properties: ${key} for ${value}`);
      const result = (target, key, value, receiver);
      // Responsive trigger view update      triggerUpdate();
      return result;
    }
  });
}
function triggerUpdate() {
  ('View Update');
}
// Exampleconst state = reactive({ name: 'Vue3', count: 0 });
(); // Access properties: name++; // Set properties: count for 1，Trigger view update

4. In-depth analysis of the working principle of v-model

Default binding and event:

In Vue3,v-modelThe default binding and event are as follows:

• Bind attributes:modelValue
• Trigger event:update:modelValue

Custom binding fields:

You can customizev-modelBound fields, for example:

<CustomInput v-model:title="titleValue" />

At this time Vue3 will resolve to:

:Title="titleValue" @update:Title="value => titleValue = value"

Subcomponents need to support customizationpropsandemit：

<script>
export default {
  props: {
    title: {
      type: String,
      required: true
    }
  },
  methods: {
    onInput(event) {
      this.$emit('update:title', );
    }
  }
};
</script>

5. Advantages of Vue3 Bidirectional Binding

Performance improvement：
useProxyAfter that, there is no need to define getter/setter separately for each property.

Increased flexibility：
v-modelSupports multiple binding fields.

Modular and clear：
By explicitpropsandemit, make data flow more transparent.

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