How do you implement two-way data binding in a Vue.js component?

To implement two-way data binding in a Vue.js component, you can use the "v-model" directive. This directive binds a value to a form input element, and updates the value whenever the input element's value changes.

Here is an example of how you might use the "v-model" directive in a Vue.js component:

<template>
  <div>
   <input v-model="message" type="text">
   <p>{{ message }}</p>
  </div>
</template>

<script>
export default {
  data() {
    return {
      message: 'Hello world!'
    }
  }
}
</script>

In this example, the value of the "message" data property is bound to the value of the input element using the "v-model" directive. When the user types in the input element, the value of the "message" data property is updated, and this change is reflected in the text displayed by the p element.