The Set constructor accepts an arbitrary number of arguments, but only the first one is used to construct the set. The remaining arguments are ignored. Code that invokes the Set constructor with multiple arguments is therefore likely to be incorrect.

Only pass a single argument to the Set constructor, which should be an iterable object (such as an array).

The following example creates a set containing the vowels in the English language, and defines a function that returns a boolean indicating whether a given character is a vowel:

However, this code does not work as intended: the Set constructor ignores all but the first argument, so the vowels set only contains the letter a.

Instead, the list of vowels should be wrapped into an array:

MDN Web Docs: Set() constructor