Non-array argument to function with destructured Array default parameters gives a TypeError

Question

I've defined the function prod which makes use of ES6's default arguments and destructuring:

function prod([a, b, c] = [1, 2, 3]) {
  console.log(a * b * c);
}

When called without arguments, it logs 6 to the console as expected.

prod() // 6

When called with an array of arguments, it logs the correct product:

prod([2, 3, 4]) // 24

When called with a number of arguments, it throws an error:

prod(2, 3, 4) // Uncaught TypeError: undefined is not a function(…)

Why does it throw an undefined is not a function error?

Edit

I understand why it throws an error. What I don't understand is why it throws that particular error.

Answer 1

The issue is that it wants an array for arguments, not 3 separate arguments. So doing this: prod([1, 2, 3]) will give you back your expected answer.

When I run prod(1, 2, 3) in Firefox I get this error: TypeError: [Symbol.iterator] is not a function.

According to the mdn docs (https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Symbol/iterator#Non-well-formed_iterables)

The function is expecting an interable object to be returned with the method @@iterator. Because that method doesn't exist (and therefore isn't a function) you're getting the is not a function error