function that checks the number of times a character is used in a string

I'm writing a function that takes a string as an argument, checks it for a given character (say "B" in this case), and then returns an integer that reflects the number of times that character appeared. I'm aware that this can be done using regex and such, but the tutorial I'm using has so far made no mention of regex. Code time:

function countBs(string) {
  var i = 0;
  var n = 0;
  var position = string.charAt(n);

  while (i < string.length) {
    if (string.charAt(n) == "B")
      n += 1;
      i++; //This line causes the following else statement to throw a syntax error. But it's the only way I can think of to have the loop continue iteration *while* checking for equivalence to "B" 
    else
      i++;
    return n;
  }

}

And then check with console.log(countBs("ABBA"));