Adding a Function to the String Prototype

One of the fun parts of JavaScript is that you can extend all the standard types by extending their prototype. In this challenge, you need to give JavaScript Strings a swapCase() function, which will return a new string with all upper case characters swapped for lower case characters, and vice versa. Any non-alphabetic characters should be kept as they are.

Examples

"Hello".swapCase() ➞ "hELLO"

"2 4 6 8 WHO DO WE APPRECIATE?".swapCase() ➞ "2 4 6 8 who do we appreciate?"

"aBcD".swapCase().swapCase() ➞ "aBcD"

Notes

• swapCase() should not alter the original string.
• Although you can add new functions to the standard data types, it's not generally a good idea in large projects!