Find the sum of all 4 digit numbers formed by taking all the digits 2, 4, 6 and 8. code example

Example 1: Write a function digitsum that calculates the digit sum of an integer. The digit sum of an integer is the sum of all its digits.

function digSum(n) {
    let sum = 0;
    let str = n.toString();
    console.log(parseInt(str.substring(0, 1)));
    for (let i = 0; i < str.length; i++) {
        sum += parseInt(str.substring(i,i+1));
        
    }
    return sum;
}

Example 2: Given a long number, return all the possible sum of two digits of it. For example, 12345: all possible sum of two digits from that number are:

function digits(num){
  let numArray = num.toString().split('');
  let sumArray = [];
  
  for (let i = 0; i < numArray.length; i++) {
    for (let j = i+1; j < numArray.length; j++) {
      let sum;
      sum = Number(numArray[i]) + Number(numArray[j]);
      sumArray.push(sum);
    }
  } 
  return sumArray;  
}