Data structures / linked lists JavaScript challenge

challenge.js

/*

# Challenge
Given the follow linked lists:
Input: l1 = [2,4,3], l2 = [5,6,4]
Do: 342 + 465 = 807
And output another linked list: [7,0,8]
--
Other example:
Input: l1 = 8,7,5, l2 = 9,0,5
Do: 578 + 509 = 1087
Output: 7801
--
Consider a linked list an object with value and next, value and next etc. until needed.
Do no write the inputs as arrays.
Consider writing the possible tests you would have done, no need to implement the test, just describe them.

# Solution
Write the solution below:
*/

solution.js

/*

# Challenge
Given the follow linked lists:
Input: l1 = [2,4,3], l2 = [5,6,4]
Do: 342 + 465 = 807
And output another linked list: [7,0,8]
--
Other example:
Input: l1 = 8,7,5, l2 = 9,0,5
Do: 578 + 509 = 1087
Output: 7801
--
Consider a linked list an object with value and next, value and next etc. until needed.
Do no write the inputs as arrays.
Consider writing the possible tests you would have done, no need to implement the test, just describe them.

# Solution
Write the solution below:
*/

// 'the inputs should be a linked list'
  // 'the input has next and value attributes'
  // 'next must be an object'
  // 'next must have the property value''
  // 'value must be a number'
  // 'it can have an optional next'

// 'output must reverse the number'
  // 'first index should be the last index of the input'
  // 'last index should be the first index of input'

// 'the method returns the first linked list with the right sorting'

const firstLinkedList = {
  value: 2,
  next: {
    value: 4,
    next: {
      value: 3
    }
  }
}

const secondLinkedList = {
  value: 5,
  next: {
    value: 6,
    next: {
      value: 4
    }
  }
}

function sumLinkedLists(l1, l2) {
  console.log(prepareLinkedList(l1))
  console.log(prepareLinkedList(l2))
  return prepareLinkedList(l1) + prepareLinkedList(l2);
}

function prepareLinkedList(l) {
  var sum = []
  let keepRunning = true;
  let currentValue = l;

  while(keepRunning) {
    sum.push(currentValue.value);

    if(currentValue.next) {
      currentValue = currentValue.next;
    } else {
      keepRunning = false;
    }
  }

  return sum.reverse();
}

console.log(sumLinkedLists(firstLinkedList, secondLinkedList))