My parameter is suddenly not defined in 'indexOf'

Question

For some reason my function parameter 'string' is defined until it gets to the 'indexOf' method, then suddenly the console it reporting it as undefined. It works fine in the rest of the statement, I just don't get it. Any help would be appreciated.

function checkRoomForItem(string) {
 for (let i = 0; i < db[0].rooms[roomLoc].roomInvent.length; i++){
  if (db[0].rooms[roomLoc].roomInvent[i] === string) { 
   console.log("String is " + string);
   inventory.push(string);
   db[0].rooms[roomLoc].roomInvent.pop(db[0].rooms[roomLoc].roomInvent.indexOf(string));
  };
 };
 displayOut();
 teleTyperOutBox("you get " + string);
}

Answer 1

Found out the problem, I was using 'pop' incorrectly, I needed to use 'splice'.