js二维数组过滤，如何不改变原数组

Question

let arr = [{
  name:1,
  data:[{
    a:'1',
    b:'2'
  }]
},
{
  name:1,
  data:[{
    a:'11',
    b:'2'
  }]
}
]
let tmpResult = []
arr.forEach((rules,index)=>{
   tmpResult[index] = rules
   tmpResult[index].data = rules.data.filter((item) => {
       return item['a'].includes('11')
   })    
})
console.log(tmpResult,arr);

打印后的arr不是原来的arr

Answer 1

let arr = [{
  name:1,
  data:[{
    a:'1',
    b:'2'
  }]
},
{
  name:1,
  data:[{
    a:'11',
    b:'2'
  }]
}
]
let tmpResult = JSON.parse(JSON.stringify(arr))
tmpResult.forEach((rules,index)=>{
   tmpResult[index] = rules
   tmpResult[index].data = rules.data.filter((item) => {
       return item['a'].includes('11')
   })    
})
console.log(tmpResult,arr);