creating sum functions as an exercise

sum.js

// Sums all "number" arguments given. This includes floats by default.
//
//   sum(1, 2, 3, 4, 5, 6, 7, 8, 9, 10); //=> 55
//   sum(1, "hey", 2, "3", 4, "five", 6, 'hi!', 7, 8.2, 9, 10); //=> 47.2
function sum() {
  var sum = 0;
  for (i = 0; i < arguments.length; i++) {
    var arg = arguments[i];
    if (typeof arg === 'number') sum += arg;
  }
  return sum;
}

sum.rb

# Sums all Numeric arguments given. Could be made to sum only Integer arguments.
# (would exclude 8.2 in the second example).
#
#   sum 1, 2, 3, 4, 5, 6, 7, 8, 9, 10 #=> 55
#   sum 1, "hey", 2, "3", 4, "five", 6, 'hi!', 7, 8.2, 9, 10 #=> 47.2
def sum(*args)
  args.inject 0 do |sum, a|
    sum += (a.is_a?(Numeric) ? a : 0)
  end
end