Convert string of character and number into integer?

I want to convert this string “F1” into an integer 1.

For example

"F1" ===> 1
"F2" ===> 2
"F3" ===> 3

So far, this is what I’ve done

parseLevel: function(level) {
    var levels = {
        "F1": 1,
        "F2": 2
    };
    return levels[level];
}

Here’s the function

parseLevel: function (level) {
  return parseInt(level, 10);
}

I’m getting an error says it’s NaN