arity in JavaScript

function subtract(first, second){
      var result = first - second;
      return result;
    document.write("arity = " + subtract.arity + "<br>")
    document.write("The result of the subtract function is: " + subtract(4,3));

Obsolete Property
This feature is obsolete. Although it may still work in some browsers, its use is discouraged since it could be removed at any time. Try to avoid using it.