arguments.length

A non-negative integer.

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.prototype.length). For example, for the function below:

function func1(a, b, c) {
  console.log(arguments.length);
}

func1.length returns 3, because func1 declares three formal parameters. However, func1(1, 2, 3, 4, 5) logs 5, because func1 was called with five arguments. Similarly, func1(1) logs 1, because func1 was called with one argument.

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

function adder(base /*, num1, …, numN */) {
  base = Number(base);
  for (let i = 1; i < arguments.length; i++) {
    base += Number(arguments[i]);
  }
  return base;
}

• Functions guide
• Functions
• arguments
• Function: length