Comment by minitech

A module doesn’t solve that kind of type confusion, though. Static typing does. The next best thing in JavaScript is passing consistent types of values to your functions, so just write

  function isPositiveInteger(x) {
      return x > 0 && Number.isInteger(x);
  }

and always pass it a number. (Of course, this shouldn’t even be a function, because JavaScript is confused about the definition of “integer” – maybe you really want `x >>> 0 === x` – and apparently is-positive-integer is confused about the definition of “positive”, so it’ll be clearer to just put things inline.)