arguments.length

The arguments.length property provides the number of arguments actually passed to a function. This can be more or less than the defined parameter's count (see Function.length).

In this example we define a function that can add two or more numbers together.

function adder(base /*, n2, ... */) {
  base = Number(base);
  for (var i = 1; i < arguments.length; i++) {
    base += Number(arguments[i]);
  }
  return base;
}

• Function
• Function.length