Why is this "Hello, World!" JavaScript code fragment recognized as an acceptable program instruction?

The actual code is:

greet = "...".toString.bind("hello world!")

Where the ... in the string literal are the bytes E2 80 AE, which is the right-to-left override Unicode character, which causes everything after it to be displayed in reverse. It's used for writing right-to-left languages like Arabic or Hebrew.

You have hidden characters which reverse the text. Here you can see the raw characters: https://www.soscisurvey.de/tools/view-chars.php