const app = Vue.createApp({
  data() {
    return {
      num: 0,
    };
  },
  methods: {
    addNum(num) {
      this.num = this.num + num;
    },
  }
});

app.component('button-counter2', {
  emits: {
    add:(num)=>{
      if(typeof num !== 'number'){
        console.warn('add事件所傳出的參數型別需為 number')
      }
      return typeof num === 'number'
    }
  },
  template: `
      <button type="button" @click="$emit('add', '1')">Emit 驗證是否為數值</button>
    `,
})
app.mount('#app');