Cash Register - cid value changes after a for loop, even though I do not touch the "cid" value whatsoever

JavaScript
1

Tell us what’s happening:

I tried the immutable approach (at least I think I did) and stayed away from mutating the original “cid” value until the very end, when I needed to copy paste the cash-in-register values. But instead of getting 0.5 pennies, I get 0 pennies. I tried debugging, which led me to discover, that something in the for loop after the switch statement changes the “cid” values globally and I cannot seem to find the solution.

Your code so far


function checkCashRegister(price, cash, cid) {
  let answer = {
    status: "",
    change: []
  };
  
  const priceCopy = price;
  const cashCopy = cash;
  const cidCopy = cid;  
  
  let totalCashInRegister = 0;
  
  let change = cashCopy - priceCopy;

  for (let i = 0; i < cidCopy.length; i++) {
    totalCashInRegister += cidCopy[i][1];
  }
  
  let totalCashInRegisterCopy = totalCashInRegister;
  
  for (let i = (cidCopy.length - 1); i >= 0; i--) {
    let currentCurrencyVal = 0;
    let val = 0;
    let currencyUnit = "";
    
    switch(i) {
      case 8:
        currentCurrencyVal = 100;
        currencyUnit = "ONE HUNDRED";
        break;
      case 7:
        currentCurrencyVal = 20
        currencyUnit = "TWENTY";
        break;
      case 6:
        currentCurrencyVal = 10;
        currencyUnit = "TEN";
        break;
      case 5:
        currentCurrencyVal = 5;
        currencyUnit = "FIVE";
        break;
      case 4:
        currentCurrencyVal = 1;
        currencyUnit = "ONE";
        break;
      case 3:
        currentCurrencyVal = 0.25;
        currencyUnit = "QUARTER";
        break;
      case 2:
        currentCurrencyVal = 0.1;
        currencyUnit = "DIME";
        break;
      case 1:
        currentCurrencyVal = 0.05;
        currencyUnit = "NICKEL";
        break;
      case 0:
        currentCurrencyVal = 0.01;
        currencyUnit = "PENNY";
        break;
    }
        
    while (Number(change.toFixed(2)) >= currentCurrencyVal && cidCopy[i][1] >= currentCurrencyVal) {
      change -= currentCurrencyVal;
      change = Number(change.toFixed(2));
      
      cidCopy[i][1] -= currentCurrencyVal;
      cidCopy[i][1] = Number(cidCopy[i][1].toFixed(2));
      
      val += currentCurrencyVal;
      val = Number(val.toFixed(2));
    }
        
    if (val !== 0) {
      answer.change = [...answer.change, [currencyUnit, val]];
    }
  }  
  
  if (change > 0) {
    answer.status = "INSUFFICIENT_FUNDS";
    answer.change = [];
  }
  
  if (change === 0) {
    let newVal = 0;
    for (let i = 0; i < answer.change.length; i++) {
      newVal += answer.change[i][1];
      newVal = Number(newVal.toFixed(2));
    }
    
    if (newVal == totalCashInRegisterCopy) {
      answer.status = "CLOSED";
      answer.change = cid;
      //  answer.change[0][1] = 0.5; <-- quick fix
    }
    
    else {
      answer.status = "OPEN";
    }
  }
  
  console.log(answer);
  
  // Here is your change, ma'am.
  return answer;
}

// Example cash-in-drawer array:
// [["PENNY", 1.01],
// ["NICKEL", 2.05],
// ["DIME", 3.1],
// ["QUARTER", 4.25],
// ["ONE", 90],
// ["FIVE", 55],
// ["TEN", 20],
// ["TWENTY", 60],
// ["ONE HUNDRED", 100]]

checkCashRegister(19.5, 20, [["PENNY", 0.5], ["NICKEL", 0], ["DIME", 0], ["QUARTER", 0], ["ONE", 0], ["FIVE", 0], ["TEN", 0], ["TWENTY", 0], ["ONE HUNDRED", 0]]);

Your browser information:

User Agent is: Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/67.0.3396.99 Safari/537.36.

Link to the challenge:
https://learn.freecodecamp.org/javascript-algorithms-and-data-structures/javascript-algorithms-and-data-structures-projects/cash-register/

3

At first I attempted with the spread operator, but the problem was still the same. Also tried the slice method, but it did not change anything either.

I have a jsbin link where I tried debugging this: https://jsbin.com/bapamogoce/1/edit?js,console

For some reason, it still mutates the original array without me ever touching it

4

I’m having a similar issue. Did you ever reach a resolution?

I also am using slice to make a “copy” of cid, and not referencing cid at all in my for loop. My console.logs show that cid goes into the loop normal, but comes out altered.

5

that is because the spread operator only copies the first level of the array and nothing beyond
(the rest are memory pointers so you end up changing the original array)

I suggest you just make a loop to copy the elements one by one (you can use spread at the lowest level)

1 Like
6

read the response above…

7

Would Object.assign() work to copy an array to a variable? Saw this in another thread, and was wondering if it would work here.

edit: nvm, I think it only works on objects

8

Excellent! That fixed it! Thank you so much…that was the only thing holding me back from passing all tests. I remember reading something about the spread operator only copying the first level, but never connected the dots.

1 Like
9

assign() can’t be used to make a deep copy either as it is only doing a shallow assignment of first level props. (I tried it to double check)

10

Thanks for checking. I figured. Plus, it’s mainly for objects anyways.