Sort() 正在改变我的原始数组。 有不同的解决方法吗？

Question

I've searched other threads and I couldn't find a working solution to my problem. I tried slice() for the array but no luck. I've got a array, first I create a copy of the original array and after a few second I overwrite one value [0][1]=555. And this affects my copy/original array, the value 1000 gets overwritten with 555. Any ideas on how to overcome this? I need to compare the two tables after the value gets changed. Here is my javascript code:

let intialstationtablevalues = [
["station name 1",75,100,100,100,100,100,100,0,100,100,100,100,1],
["station name 2",200,220,100,100,100,100,100,2,100,100,100,100,2],
["station name 3",300,110,100,100,100,100,100,0,100,100,100,760,3],
["station name 4",400,100,109,100,100,100,100,3,100,100,100,100,4],
["station name 5",500,100,100,100,100,100,100,0,100,100,100,100,5],
["station name 6",600,130,134,100,100,100,100,2,100,100,100,340,6],
["station name 7",700,100,100,100,100,100,100,0,100,100,100,100,7],
["station name 8",800,200,340,100,100,100,100,5,100,100,100,10,8],
["station name 9",900,100,100,100,100,100,100,0,100,100,100,6,9],
["station name 10",1000,100,900,100,100,100,100,2,100,100,100,100,10],
];
let old = []
let copy = []


setInterval(read,2000)
setTimeout(changevalue,10000)

function changevalue(){
  console.log("value changed")
  intialstationtablevalues[0][1]=555;
}


function read(){
        if(copy==""){
            copy = intialstationtablevalues.slice()
      }
        sortnow = intialstationtablevalues.sort(function(a,b){
            return b[1]-a[1];
        })

        console.log("sortnow",sortnow)

        if(old==""){
            copy.forEach(function(item,index){
                old.push(item)
            })
            old.sort(function(a,b){
                return b[1]-a[1];
            })
        }

        console.log("old",old)
}

Answer 1

sortedArray = [...arrayYouWantToSort].sort() Spreading the array you want to copy into a new array and then sort that array. Fun way to do it!

sortedArray = [...arrayYouWantToSort];
sortedArray[0][1] = whatever // whatever you wanna change
sortedArray.sort()

The main point is that spreading the arrayYouWantToSort into a new array literal creates a new array in memory. So arrayYouWantToSort and sortedArray are now total different physical parts of memory, but they have the same 'values'. So you can change values in one without affecting the other.

So you first create the copied array, and then mutate the new array.

Answer 2

I think.slice() is working fine here, try to replace the if statment with

if(copy.length ===0)

to check the empty array