Implement v-model Correctly in Render Functions

Impact: MEDIUM - When using v-model on components in render functions, you must manually handle both the modelValue prop and the update:modelValue event. Missing either part breaks two-way binding.

In templates, v-model is syntactic sugar that expands to a modelValue prop and an update:modelValue event listener. In render functions, you must implement this expansion manually.

Task Checklist

Pass modelValue as a prop for the bound value
Pass onUpdate:modelValue handler to receive updates
For named v-models, use the corresponding prop and event names
Use emit in child components to trigger updates

Incorrect:

import { h } from 'vue';
import CustomInput from './CustomInput.vue';

export default {
  setup() {
    const text = ref('');

    return () =>
      h(CustomInput, {
        // WRONG: Missing the update handler
        modelValue: text.value,
      });
  },
};

import { h } from 'vue';
import CustomInput from './CustomInput.vue';

export default {
  setup() {
    const text = ref('');

    return () =>
      h(CustomInput, {
        // WRONG: Wrong event name format
        modelValue: text.value,
        onModelValueUpdate: (val) => (text.value = val),
      });
  },
};

Correct:

import { h, ref } from 'vue';
import CustomInput from './CustomInput.vue';

export default {
  setup() {
    const text = ref('');

    return () =>
      h(CustomInput, {
        // CORRECT: modelValue prop + onUpdate:modelValue handler
        modelValue: text.value,
        'onUpdate:modelValue': (value) => (text.value = value),
      });
  },
};

Native Input Elements

For native inputs, use value and onInput:

import { h, ref } from 'vue';

export default {
  setup() {
    const text = ref('');

    return () =>
      h('input', {
        value: text.value,
        onInput: (e) => (text.value = e.target.value),
      });
  },
};

Named v-models (Multiple v-models)

import { h, ref } from 'vue';
import UserForm from './UserForm.vue';

export default {
  setup() {
    const firstName = ref('');
    const lastName = ref('');

    return () =>
      h(UserForm, {
        // v-model:firstName
        firstName: firstName.value,
        'onUpdate:firstName': (val) => (firstName.value = val),

        // v-model:lastName
        lastName: lastName.value,
        'onUpdate:lastName': (val) => (lastName.value = val),
      });
  },
};

v-model with Modifiers

Handle modifiers in the child component:

import { h, ref } from 'vue'
import CustomInput from './CustomInput.vue'

// Parent - passing modifier
export default {
  setup() {
    const text = ref('')

    return () => h(CustomInput, {
      modelValue: text.value,
      'onUpdate:modelValue': (val) => text.value = val,
      modelModifiers: { trim: true, capitalize: true }
    })
  }
}

// Child - handling modifier
export default {
  props: ['modelValue', 'modelModifiers'],
  emits: ['update:modelValue'],
  setup(props, { emit }) {
    const handleInput = (e) => {
      let value = e.target.value

      if (props.modelModifiers?.trim) {
        value = value.trim()
      }
      if (props.modelModifiers?.capitalize) {
        value = value.charAt(0).toUpperCase() + value.slice(1)
      }

      emit('update:modelValue', value)
    }

    return () => h('input', {
      value: props.modelValue,
      onInput: handleInput
    })
  }
}

JSX Syntax

import { ref } from 'vue';
import CustomInput from './CustomInput.vue';

export default {
  setup() {
    const text = ref('');
    const count = ref(0);

    return () => (
      <div>
        {/* v-model on custom component */}
        <CustomInput modelValue={text.value} onUpdate:modelValue={(val) => (text.value = val)} />

        {/* v-model on native input */}
        <input value={text.value} onInput={(e) => (text.value = e.target.value)} />

        {/* Named v-model */}
        <Counter count={count.value} onUpdate:count={(val) => (count.value = val)} />
      </div>
    );
  },
};

Creating v-model-compatible Components

import { h } from 'vue';

export default {
  props: {
    modelValue: String,
  },
  emits: ['update:modelValue'],
  setup(props, { emit }) {
    return () =>
      h('input', {
        value: props.modelValue,
        onInput: (e) => emit('update:modelValue', e.target.value),
      });
  },
};

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