How is it possible for this variable to be altered without any modifications made to it in the current function?

Question

How is it possible for this variable to be altered without any modifications made to it in the current function?

This particular function receives two arrays as input: arrOne, which is an array comprising arrays of numbers, and arrTwo, which is an array containing numbers. My goal here is to generate every possible combination, followed by obtaining the unique combinations. However, I've encountered a stumbling block.

function multOrdProduct(arrOne,arrTwo){
  let backSet = [];
  let count = 0;
  let tempArr = new Array(arrOne.length);
  let permArrOne = [];
  let permArrTwo = [];
  let pushed;
  let setPart = [];
  
  for(i=0; i < arrOne.length; i++){
    permArrOne.push(arrOne[i]);
  }
// ^sets permArrOne to equal the same array as ArrOne
  
  for(i = 0; i < arrOne.length;i++){
    for(j = 0; j < arrTwo.length; j++){

      setPart = permArrOne[i];
      
      console.log(permArrOne[i]);
      
      setPart.push(arrTwo[j]);
      backSet.push(setPart);
    }
  }
  return backSet;
}

I initially believed that permArrOne[i] would remain unchanged since no value assignment is made to it. Can anyone explain why it changes in each iteration?

javascript arrays function variables

Answer 1

Answer №1

When you reference permArrOne in setPart without cloning it, any changes made to setPart will also affect permArrOne.

.slice() is a method that can be used to create a new array:

function multiplyArrays(arr1,arr2){
  let backSet = [];
  let count = 0;
  let tempArr = new Array(arr1.length);
  let permArr1 = [];
  let permArr2 = [];
  let pushed;
  let setPart = [];
  
  for(i=0; i < arr1.length; i++){
    permArr1.push(arr1[i]);
  }
// ^sets permArr1 to be the same as arr1
  
  for(i = 0; i < arr1.length;i++){
    for(j = 0; j < arr2.length; j++){

      setPart = permArr1[i].slice();
      
      console.log(permArr1[i]);
      
      setPart.push(arr2[j]);
      backSet.push(setPart);
    }
  }
  return backSet;
}

let array1 = [[0, 1], [1, 2]]

let array2 = [0, 1, 2]

multiplyArrays(array1, array2)

Answer 2

When you reference permArrOne in setPart without cloning it, any changes made to setPart will also affect permArrOne.

.slice() is a method that can be used to create a new array:

function multiplyArrays(arr1,arr2){
  let backSet = [];
  let count = 0;
  let tempArr = new Array(arr1.length);
  let permArr1 = [];
  let permArr2 = [];
  let pushed;
  let setPart = [];
  
  for(i=0; i < arr1.length; i++){
    permArr1.push(arr1[i]);
  }
// ^sets permArr1 to be the same as arr1
  
  for(i = 0; i < arr1.length;i++){
    for(j = 0; j < arr2.length; j++){

      setPart = permArr1[i].slice();
      
      console.log(permArr1[i]);
      
      setPart.push(arr2[j]);
      backSet.push(setPart);
    }
  }
  return backSet;
}

let array1 = [[0, 1], [1, 2]]

let array2 = [0, 1, 2]

multiplyArrays(array1, array2)

How is it possible for this variable to be altered without any modifications made to it in the current function?

Answer №1

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