computed

<template>
  <el-form ref="form" :model="form" label-width="80px">
    <el-form-item label="a">
      <el-input v-model="form.a"></el-input>
    </el-form-item>
    <el-form-item>
      <el-button type="primary" @click="onSubmit">a++</el-button>
    </el-form-item>
  </el-form>
</template>
<script>
export default {
  name: ‘couponForm‘,
  computed: {
    formData () {
      return {
        a: this.form.a
      }
    }
  },
  watch: {
    formData: {
      deep: true,
      handler (newVal, oldVal) {
        console.log(‘newVal‘, newVal) // {a:1}
        console.log(‘oldVal‘, oldVal) // {a:1}
        console.log(‘newVal===oldVal？‘, newVal === oldVal) // false
        console.log(‘newVal==oldVal？‘, JSON.stringify(newVal) === JSON.stringify(oldVal)) // true
      }
    }
  },
  data () {
    return {
      form: {
        a: 1
      }

    }
  },
  methods: {
    onSubmit () {
      this.form.a = this.form.a + 1
      this.form.a = this.form.a - 1
    }
  }
}
</script>