Modify copied array without modifying the original array js [duplicate]

Question

function checkCashRegister(price, cash, cid) {
  let payBackAmount = cash - price;
  let tempArr = cid.slice();

  for (let i = 0; i < tempArr.length; i++) {
    tempArr[i][1] = 0;
  }
  console.log("cid is", cid);
}
checkCashRegister(19.5, 20, [
  ["PENNY", 1.01],
  ["NICKEL", 2.05],
  ["DIME", 3.1],
  ["QUARTER", 4.25],

  ["ONE", 90],
  ["FIVE", 55],
  ["TEN", 20],
  ["TWENTY", 60],
  ["ONE HUNDRED", 100],
]);

Here I am trying to copy an array from the parameterized function. cid is the array which I am trying to pass inside the function and I am trying to copy it into tempArr. Later when modifying the values of tempArr , the values of cid is changing as well. I have also tried copying the values using let tempArr=[...cid] and let tempArr=cid.slice(0)

You made a shalow copy, not a deep one. cid (great naming by the way :D) is a 2d array. If you add or remove elements from tempArr, the changes won't occur on cid, however, the elements of the array are still references, since they are arrays too. A quick and dirty way to do that is const tempArr = JSON.parse(JSON.stringify(cid)); — Cid
– Cid, Commented Nov 17, 2021 at 10:37
@Cid Thanks a lot for your explanation and the link. I really thought copying would be same since I was just trying to copy the contents of an array. — Ishan Sahu
– Ishan Sahu, Commented Nov 17, 2021 at 10:47

Sai Krishna · Accepted Answer · 2021-11-17 10:44:24Z

3

Here in the above code when you are copying one array to an other array the slice method and spread operator from javascript does a shallow copy, for your usecase you might want to do a deep clone of the object you can do let tempArr = JSON.parse(JSON.stringify(cid)) , instead of this you can also use deepClone from Lodash to deep clone a object

also please look at this thread What is the difference between a deep copy and a shallow copy? to know more about shallow clone and deep clone

answered Nov 17, 2021 at 10:44

Sai Krishna

812 bronze badges

Sign up to request clarification or add additional context in comments.

Collectives™ on Stack Overflow

Modify copied array without modifying the original array js [duplicate]

1 Answer 1

Comments

Linked

Hot Network Questions

Collectives™ on Stack Overflow

1 Answer 1

Comments

Linked

Related