U+2028 and U+2029 end a JavaScript line comment and break a regex literal, though string literals accept them

Fact

LINE SEPARATOR (U+2028) and PARAGRAPH SEPARATOR (U+2029) are line terminators in JavaScript source, exactly like \n. Since ES2019 they are allowed raw inside string literals, but everywhere else they still end the line:

• In a regular expression literal, /[<U+2028>]/ is a SyntaxError: "Invalid regular expression: missing /".
• In a // comment, everything after the character is code again: let x = 1; // x<U+2028>x = 2; runs x = 2.

Both characters are invisible in editors, diffs and terminals.

Why it matters

They arrive by copy-paste from documents and web pages, and from tooling that turns a \u2028 escape into the raw character. The error points at a line that looks complete, and the comment case is worse: no error at all, just a statement that executes although it reads as commented out.

How to apply

• Write these characters as escapes: \u2028 inside a regex or string, or build the character class with String.fromCharCode / a code-point check.
• To find them: grep -nP '[\x{2028}\x{2029}]' -r src/.
• Code that filters them (sanitising names, for example) is safest as a code-point comparison rather than a regex containing them.