1 /(?:[^[#\s\\]+|\\(?:[\S\s]|$)|\[\^?]?(?:[^\\\]]+|\\(?:[\S\s]|$))*]?)+|(\s*#[^\n\r\u2028\u2029]*\s*|\s+)([?*+]|{[0-9]+(?:,[0-9]*)?})?/g 2 /{[0-9]+}?/g 3 {123} 4 {a} 5 f{a} 6 f 7 SyntaxError 8 SyntaxError