Finding the symmetric difference between two arrays

Question

I need to find any differences between two arrays in the elements and push said elements onto a new array that is then returned in the end. I have pulled a function from this website through searching that has the intended purpose of counting the number of times an element occurs in an array and returning that. First I have concatenated the two arrays together, then applied this function (modified it to fit my problem as well as I could). I then tried to push the elements that were different (didn't occur twice) to the new array. My code of course doesn't work and I am also new to Javascript, so please be easy on me.

Below is some code of what I have tried, which doesn't pass any tests:

function diffArray(arr1, arr2) {
  var newArr = [];

  let tempArr = arr1.concat(arr2);

  function countInArray(array, what) {
    var count = 0;
    for (var i = 0; i < array.length; i++) {
        if (array[i] === what) {
            count++;
        }
    }
    if (countInArray(tempArr, tempArr[i]) < 2) {
      newArr.push(tempArr[i]);
    } 
}


  return newArr;
}

If you provide any code please try to break it down for me so that I can understand better and learn.

Answer 1

To achieve expected result, use below option by making few changes to your code

1. Return count for countInArray (currently it returns undefined)

function countInArray(array, what) { var count = 0; for (var i = 0; i < array.length; i++) { if (array[i] === what) { count++; } } return count }

2. Remove calling countInArray inside countInArray method
3. Run For Loop for tempArr to compare with other each value of tempArr

for (var j = 0; j < tempArr.length; j++) { if (countInArray(tempArr, tempArr[j]) < 2) { newArr.push(tempArr[j]); } }

Working code :

function diffArray(arr1, arr2) {
  let tempArr = arr1.concat(arr2);
  let newArr = [];
  function countInArray(array, what) {
    var count = 0;
    for (var i = 0; i < array.length; i++) {
        if (array[i] === what) {
            count++;
        }
    }
    return count
}
  
    for (var j = 0; j < tempArr.length; j++) {
       if (countInArray(tempArr, tempArr[j]) < 2) {
         newArr.push(tempArr[j]);
       } 
    }


  return newArr;
}


let arr1 = ["diorite", "andesite", "grass", "dirt", "pink wool", "dead shrub"]
let arr2 = ["diorite", "andesite", "grass", "dirt", "dead shrub"]
console.log(diffArray(arr1, arr2))

let arr3 = [1, "calf", 3, "piglet"]
let arr4 =  [7, "filly"]
console.log(diffArray(arr3, arr4))

codepen - https://codepen.io/nagasai/pen/OYNdZX?editors=1010