JavaScript / Using system generated regex for validation

Question

we want to use regex to validate a document structure. For this we simplify the document and the regex. The regex is generated out of a schema which is used for the validation. The application is completly client based and coded in JavaScript.

A simple example is this regex:

regex1 = new RegExp(/~(A{1}B?C?(D*|E*|F*|G*)+){1}~/g)

That means the document structure can have this structure

A
-B
-D
-D
-D
-D
-D

So the document structure is parsed to ~ABDDDDD~

Now I want to validate if I can add "A" to the end which would result in this string: ~ABDDDDDA~

This does not match with the reg ex anymore:

"~ABDDDDDA~".match(regex1)

This does work quiet fine, but the document structure can grow and be like this: ~ABDDDDDDDDDDDDDDDDDDDDDDDDDDDDDDDDDDDDDDDDDDDDDDDDDD~

A matching value can be matched quiet fast, but if the value is then: ~ABDDDDDDDDDDDDDDDDDDDDDDDDDDDDDDDDDDDDDDDDDDDDDDDDDDA~

It takes very long, most times I just close the browser and reopen it.

Does anyone have ideas how to solve it?

Thanks!

UPDATE

The RegEx should also cover more, the structure can be quiet dynamic. I have not used a RegEx Generator, this example is parsed from a self developed script and is just an example.

It is in this case, that there is one root element A, then optional B or C. And now in a not given order any amount of D,E,F,G. But at least one!

So it should be valid for: "~ABDDDDDFEG~" "~AGGGGGEGGD~" "~ABCDEFG~" "~ABCDDDDDDDDDDDDDDDEFGGGGGG~"

Additionally it is possible, that that the E is limited to 0-5 occurances.

As soon as I work with the match either(A | B), there are real performance issues in all browsers. (IE, Chrome, Firefox)

Any ideas? Are there any alternatives to "match either(A | B)" with better performance?

What is your question? Your regex seems to do the job... is it the running time? — Yossi Vainshtein
– Yossi Vainshtein, Commented Jan 30, 2018 at 13:48
This is the case of catastrophic backtracking. You need to fix your regex generator. — georg
– georg, Commented Jan 30, 2018 at 13:49
If you want help fixing your Regex generator, you should post some info about it. — Adrien Brunelat
– Adrien Brunelat, Commented Jan 30, 2018 at 13:53

Adrien Brunelat · Accepted Answer · 2018-01-30 13:57:07Z

1

The resulting regex should be as close as possible to:

~AB?C?[DEFG]*A?~

There are a lot of simplifications to do in your regex generator to get rid of the following points:

{1}: is literally useless, you can remove it from everywhere
(A*|B*)+: is strictly equivalent to [AB]*

Here is a Regex101: https://regex101.com/r/Lc6Fx8/1

Also, if you want help fixing your Regex generator, you should post some info about it.

edited Jan 30, 2018 at 13:57

answered Jan 30, 2018 at 13:48

Adrien Brunelat

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