SyntaxError: raw bracket is not allowed in regular expression with unicode flag

SyntaxError: Invalid regular expression: /{/u: Lone quantifier brackets (V8-based)
SyntaxError: raw bracket is not allowed in regular expression with unicode flag (Firefox)
SyntaxError: Invalid regular expression: incomplete {} quantifier for Unicode pattern (Safari)
SyntaxError: Invalid regular expression: unmatched ] or } bracket for Unicode pattern (Safari)

In Unicode-unaware mode, {, }, and ] that are not part of a quantifier or character class are treated as literal characters. This may hide errors in your code and is therefore deprecated and disallowed in Unicode-aware mode. You should either check whether you have invalid syntax or you should escape the characters to match them literally.

If { appears in a context that accepts a quantitier, it is treated as the start of a quantifier. If what follows it is not a valid quantifier, another syntax error, incomplete quantifier, is thrown.

• Regular expressions
• Character class: [...], [^...]
• Character escape: \n, \u{...}
• Quantifier: *, +, ?, {n}, {n,}, {n,m}