The fast/regex/pcre-test-1 layout test fails with YARR Interpreter: FAIL regex269.exec(input0); should be 12-sep-98. Was null. The test case is: regex269 = /(?=[^a-z]+[a-z])\d{2}-[a-z]{3}-\d{2}|(?![^a-z]+[a-z])\d{2}-\d{2}-\d{2}/; var input0 = "12-sep-98"; It seems when a parenthetical assertion contains a term with a quantifier (+ or *) the YARR Interpreter doesn't match the subpattern correctly. Here is a simpler example: var str = "aab".match(/(?=a+b)aab/); result: null expected: aab These kind of patterns work well with YARR JIT.
These test cases have all since been fixed in the YARR interpreter.