JavaScriptTypeScriptEditor does not support text selection, cut, copy, or paste.
This is because it does not support a keyboard.
It's a cliché, but: How did this get past App Review?
After 5 minutes use, the keyboard became erratic (tap in the editor, the keyboard appears and immediately disappears). Soon thereafter the keyboard was never presented at all. At first, double (word) and triple (line) taps were ignored. Then single-taps were ignored; no keyboard, no selection.
The "support" website advertises the developer's cross-platform development services. No mention of JavaScriptTypeScriptEditor, much less support for it. I infer this is meant to showcase the quality of its work. Noted.
The idea that the best glyph for a "run" button was "send email" should have been a hint. The "solution" for suppressing typographic quotes by putting it on the customer to sacrifice them system-wide is, um, surprising, given that filtering insertions in individual UITextFields has been UIKit 101 for fifteen years. (I smell "cross-platform solution." Noted.)
I purchased in haste because the ads were too obstructive to properly assess the free version, and I was too eager to have an iPod REPL. Lesson learned.