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Vue 3.0 Style Guide

Vue 3.0 access this in default function of prop

In Vue 3, you are not able to directly access the Vue instance (this) within the default function of a prop. This is because the prop's default function is evaluated before the Vue instance is fully created.

If you need to access other data within a component while defining default prop values, consider using a computed property or a method instead. If you have data that should change based on props, you can use a computed property. If you need to perform an operation based on a prop, you can use a method.

Here is an example where a computed property is used to derive a value based on a prop:

<template>
  <div>
    <p>{{ computedMessage }}</p>
  </div>
</template>

<script>
export default {
  props: {
    message: {
      type: String,
      default: 'Hello',
    },
  },
  computed: {
    computedMessage() {
      return `${this.message}, Vue!`;
    },
  },
};
</script>

In this example, computedMessage is a computed property that depends on the message prop. It will automatically update whenever message changes.

If you still feel the need to use this in the default function of a prop (which is generally not recommended), a common pattern is to use a factory function to return the default value. However, keep in mind that the returned value is not reactive:

export default {
  props: {
    someProp: {
      type: Object,
      default: function () {
        return {
          // You can't refer to `this` here
        };
      },
    },
  },
};

In general, it's best to avoid relying on this in the default function of a prop and instead use computed properties, methods, or factory functions to generate default prop values.

Vue 3.0 Access 'this' in Default Prop Function:

In Vue 3.0, you can access the component instance (this) within a default prop function. This allows you to dynamically compute the default value based on the component's state.

<!-- AccessThisInPropDefault.vue -->
<template>
  <div>{{ dynamicProp }}</div>
</template>

<script>
export default {
  props: {
    dynamicProp: {
      default() {
        // Accessing 'this' inside the default prop function
        return this.someMethod();
      },
    },
  },
  methods: {
    someMethod() {
      return 'Dynamic Value';
    },
  },
};
</script>

Vue 3.0 Default Prop Value with Access to Component Instance:

Use this to access the component instance within the default prop function and compute the default value based on the component's properties or methods.

<!-- DefaultPropAccess.vue -->
<template>
  <div>{{ defaultPropValue }}</div>
</template>

<script>
export default {
  props: {
    defaultPropValue: {
      default() {
        // Accessing 'this' to compute the default value
        return this.someMethod() + ' Default';
      },
    },
  },
  methods: {
    someMethod() {
      return 'Dynamic Value';
    },
  },
};
</script>

Vue 3.0 Using 'this' in Default Prop Function:

Leverage this to access the component instance and utilize its methods or properties to compute the default value for a prop.

<!-- UsingThisInPropDefault.vue -->
<template>
  <div>{{ computedDefault }}</div>
</template>

<script>
export default {
  props: {
    computedDefault: {
      default() {
        // Using 'this' to access the component instance
        return this.someMethod() + ' Default';
      },
    },
  },
  methods: {
    someMethod() {
      return 'Dynamic Value';
    },
  },
};
</script>

Vue 3.0 Prop Default Function and Component Context:

Access the component context through this in the default prop function to compute the default value based on the component's state.

<!-- PropDefaultAndContext.vue -->
<template>
  <div>{{ dynamicProp }}</div>
</template>

<script>
export default {
  props: {
    dynamicProp: {
      default() {
        // Accessing component context to compute the default value
        return this.someData + ' Default';
      },
    },
  },
  data() {
    return {
      someData: 'Dynamic Value',
    };
  },
};
</script>

Vue 3.0 Accessing Component Instance in Prop Default:

Utilize this in the default prop function to access the component instance and dynamically compute the default value based on component properties or methods.

<!-- ComponentInstanceInPropDefault.vue -->
<template>
  <div>{{ dynamicProp }}</div>
</template>

<script>
export default {
  props: {
    dynamicProp: {
      default() {
        // Accessing the component instance to compute the default value
        return this.someMethod();
      },
    },
  },
  methods: {
    someMethod() {
      return 'Dynamic Value';
    },
  },
};
</script>

Vue 3.0 Dynamic Prop Defaults with 'this' Reference:

Reference this inside the default prop function to dynamically compute default values based on the component's state.

<!-- DynamicPropDefaults.vue -->
<template>
  <div>{{ dynamicProp }}</div>
</template>

<script>
export default {
  props: {
    dynamicProp: {
      default() {
        // Dynamic prop default based on 'this' reference
        return this.someData + ' Default';
      },
    },
  },
  data() {
    return {
      someData: 'Dynamic Value',
    };
  },
};
</script>

Vue 3.0 Prop Default Function and Instance Methods:

Access this within the default prop function to invoke instance methods and compute the default value dynamically.

<!-- PropDefaultAndMethods.vue -->
<template>
  <div>{{ dynamicProp }}</div>
</template>

<script>
export default {
  props: {
    dynamicProp: {
      default() {
        // Invoking instance methods using 'this' in prop default
        return this.someMethod();
      },
    },
  },
  methods: {
    someMethod() {
      return 'Dynamic Value';
    },
  },
};
</script>

Vue 3.0 Using 'this' in Prop Default for Dynamic Values:

Leverage this in the default prop function to access the component instance and compute dynamic default values based on the component's state.

<!-- UsingThisInPropDefault.vue -->
<template>
  <div>{{ dynamicProp }}</div>
</template>

<script>
export default {
  props: {
    dynamicProp: {
      default() {
        // Using 'this' to compute dynamic default values
        return this.someData + ' Default';
      },
    },
  },
  data() {
    return {
      someData: 'Dynamic Value',
    };
  },
};
</script>

Vue 3.0 Passing Component Instance to Default Prop Function:

Pass the component instance explicitly to the default prop function to access its context and compute dynamic default values.

<!-- PassInstanceToPropDefault.vue -->
<template>
  <div>{{ dynamicProp }}</div>
</template>

<script>
export default {
  props: {
    dynamicProp: {
      default(vm) {
        // Explicitly passing component instance to compute default value
        return vm.someData + ' Default';
      },
    },
  },
  data() {
    return {
      someData: 'Dynamic Value',
    };
  },
};
</script>

Vue 3.0 Prop Default Function and Component Lifecycle:

Access the component's lifecycle methods using this within the default prop function to compute default values based on the component's state.

<!-- PropDefaultAndLifecycle.vue -->
<template>
  <div>{{ dynamicProp }}</div>
</template>

<script>
export default {
  props: {
    dynamicProp: {
      default() {
        // Accessing component lifecycle to compute default value
        return this.$options.name + ' Default';
      },
    },
  },
};
</script>