Corresponding Regexp In Javascript

Question

I have the following regexp which should detect sequential digits like "123456" or "654321"in c# but cannnot convert it to the corresponding javascript regexp string.

string re = @"(?x)
        ^
        # fail if...
        (?!
            # sequential ascending
            (?:0(?=1)|1(?=2)|2(?=3)|3(?=4)|4(?=5)|5(?=6)|6(?=7)|7(?=8)|8(?=9)){5} \d $
            |
            # sequential descending
            (?:1(?=0)|2(?=1)|3(?=2)|4(?=3)|5(?=4)|6(?=5)|7(?=6)|8(?=7)|9(?=8)){5} \d $
        )
    ";

I tried the following Javascript but it seems to always return true:

var re = new RegExp("^(?!(?:0(?=1)|1(?=2)|2(?=3)|3(?=4)|4(?=5)|5(?=6)|6(?=7)|7(?=8)|8(?=9)){5} \d $|(?:1(?=0)|2(?=1)|3(?=2)|4(?=3)|5(?=4)|6(?=5)|7(?=6)|8(?=7)|9(?=8)){5} \d $)");
var isMatch = re.test(str);

@WiktorStribiżew I did but it still tests true for both "123456" and "135468". — John L.
– John L., Commented Feb 6, 2017 at 23:20
123456 does not match, and 135468 looks valid as per the regex. Same results are obtained at regexstorm.net/tester — Wiktor Stribiżew
– Wiktor Stribiżew, Commented Feb 6, 2017 at 23:22
@WiktorStribiżew Apparently I needed to double the back-slashes as they were evaluated as escape characters. — John L.
– John L., Commented Feb 6, 2017 at 23:32
Why not just use a function that process the string letter by letter? — ibrahim mahrir
– ibrahim mahrir, Commented Feb 6, 2017 at 23:33

Wiktor Stribiżew · Accepted Answer · 2017-02-06 23:38:34Z

1

Since the JavaScript regex engine does not support freespace (verbose) regex mode (enabled with the (?x) inline modifier) you need to remove all the formatting whitespace from the pattern.

In JS, you'd better use a regex literal notation to avoid the trouble of choosing the right number of backslashes to escape special regex metacharacters:

var re = /^(?!(?:0(?=1)|1(?=2)|2(?=3)|3(?=4)|4(?=5)|5(?=6)|6(?=7)|7(?=8)|8(?=9)){5}\d$|(?:1(?=0)|2(?=1)|3(?=2)|4(?=3)|5(?=4)|6(?=5)|7(?=6)|8(?=7)|9(?=8)){5}\d$)/;

answered Feb 6, 2017 at 23:38

Wiktor Stribiżew

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