Google Apps Script - TypeError: Cannot read property 'length' of undefined

Question

I have a Google Sheets script that is supposed to grab data from an API but I am getting the error

TypeError: Cannot read property 'length' of undefined (line 5, file "draftOrder")

How can I fix this error? I haven't touched this script in years, so I'm not sure what broke.

  function draftOrder(ownerRange, numRounds) {
  var output = [];
  var owners = [];

  for (var i = 0; i < ownerRange.length; i++) {
    if (ownerRange[i][0] !== '') {
      owners.push(ownerRange[i][0]); 
    }
  }

  for (var i = 0; i < numRounds; i++) {
    if (i % 2 == 0) {
      output = output.concat(owners);
    } else {
      output = output.concat([].concat(owners).reverse());
    }

  }
  return output;
}

Thanks in advance for any help that you can provide. Cheers!

Answer 1

function draftOrder(ownerRange, numRounds) {
  var output = [];
  var owners = [];
  if(ownerRange && numRounds) {//checking for valid inputs

    for (var i = 0; i < ownerRange.length; i++) {
      if (ownerRange[i][0] !== '') {
        owners.push(ownerRange[i][0]); 
      }
    }

    for (var i = 0; i < numRounds; i++) {
      if (i % 2 == 0) {
        output = output.concat(owners);
      } else {
        output = output.concat([].concat(owners).reverse());
      }

    }
    return output;
  }else{
    SpreadsheetApp.getUi().alert('Invalid Inputs')
  }
}