Watch 와 Computed 차이.

• Computed Properties: Use when you want to calculate or derive a value based on existing data. They are synchronous and return a value.
• Watchers: Use when you need to perform asynchronous or complex operations in response to changes in data. They allow you to react to changes but don't return a value directly.

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

<script>
export default {
  data() {
    return {
      firstName: 'John',
      lastName: 'Doe'
    };
  },
  computed: {
    fullName() {
      return `${this.firstName} ${this.lastName}`;
    }
  }
};
</script>

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

<script>
export default {
  data() {
    return {
      count: 0,
      message: ''
    };
  },
  watch: {
    count(newValue, oldValue) {
      this.message = `Count changed from ${oldValue} to ${newValue}`;
    }
  }
};
</script>

한글로 하면 리턴이 있냐 없냐의 차이인가? 그리고 watch는 old나 new가 있고? 둘다 지정한 값이 변하면 내부 function이 작동한다.