el-input输入后 targetDateValsBackUp里面的period1也发生了改变 这是什么原理呢

Question

data() {
  return {
    targetDateVals: {
      period1: '',
    },
    targetDateValsBackUp: {},
  };
}

methods: {
    const targetDateVals = {
      period1: '1',
    }
    this.targetDateVals = targetDateVals
    this.targetDateValsBackUp = {...targetDateVals}
}

<el-input v-model="targetDateVals.period1"></el-input>