watch-vue2.vue

<template>
  <div>
    <input type="text" v-model="name" />
  </div>
</template>

<script>
export default {
  data(){
    return {
      name: null,
    }
  },
  watch: {
    name(newVal, oldVal){
      console.log(`${newVal} ${oldVal}`);
    }
  }
};
</script>