I'm currently working on a program in node, and part of my code looks like this:

function interpretRange(num, shorthand) {
  let shorthandLength = shorthand.length
  console.log(typeof num);
  console.log(num.length);
  ...

When I run this code, passing '1' as the argument for num, I see the following in my console:

string
1
undefined
/Users/username/Documents/10. Programming/problem 4.js:78
  console.log(num.length);
                 ^
TypeError: Cannot read property 'length' of undefined

Any idea why this error could be happening? As you can see, i checked for the type of num and it's a string. And then when I print num to the console it works and prints 1 which is correct.

However, for some reason I'm still getting the type error (even after the value was printed to the console).

Edit: Full Code Here:

The error happens at num.length

function completeNumbers(shorthand) {
  let ranges = shorthand.split(', ');
  let longHand = [];
  ranges.forEach(range => { 
    let interpreted = [];
    let expanded = [];
    range.split(/[-:..]/g)
         .reduce((curr, shorthand) => { // What hapens if it's one number
           interpreted.push([curr, interpretRange(curr, shorthand)])
         })
    console.log(interpreted);
    interpreted.forEach(range => expanded.push(expandList(range)))
    console.log(expanded)
  })
}

function interpretRange(num, shorthand) {
  let shorthandLength = shorthand.length
  let baseNum = num.length === shorthand.length ? '0' : num.slice(0, -shorthandLength)
  let compareNum = num.slice(-shorthandLength);
  if (parseInt(shorthand) <= parseInt(compareNum)) {
    return String(parseInt(baseNum) + 1) + shorthand;
  } else {
    return baseNum + shorthand;
  }
};


completeNumbers("1:5:2, 3"); // 1, 2, 3, 4, 5, 6, ... 12