Improving Regexp performance

Question

I have the following Regex code that's taking a long time (30+ seconds) to validate large URLS:

let validReg = new RegExp('^(https?:\\/\\/)?'+ // protocol '((([a-z\\d]([a-z\\d-]*[a-z\\d])*)\\.)+[a-z]{2,}|'+ // domain name '((\\d{1,3}\\.){3}\\d{1,3}))'+ // OR ip (v4) address '(\\:\\d+)?(\\/[-a-z\\d%_.~+]*)*'+ // port and path '(\\?[;&a-z\\d%_.~+=-]*)?'+ // query string '(\\#[-a-z\\d_]*)?$','i'); let isValid = validReg.test(component.repository_url);

How can I change this code to validate the same Regex more efficiently?

If it was Python, you'd skip the regex and use a dedicated URL parsing API, e.g. urllib.parse.urlparse. Parsing complicated formats with a regex is typically a terrible idea (even if it works, it's rarely maintainable). — ShadowRanger
– ShadowRanger, Commented Mar 6, 2022 at 3:46
@BrokenBenchmark thanks for pointing out the mistake. this is Javascript. — web-dev-nerd
– web-dev-nerd, Commented Mar 6, 2022 at 7:04
Since it is JavaScript one would use parser based approaches as well ... the Web API provides URL and URLSearchParams — Peter Seliger
– Peter Seliger, Commented Mar 6, 2022 at 11:33
Does this answer your question? What is the best regular expression to check if a string is a valid URL? — Peter Seliger
– Peter Seliger, Commented Mar 6, 2022 at 13:42

Wiktor Stribiżew · Accepted Answer · 2022-03-06 12:20:58Z

You need to refactor the part where you match hyphen separated word chars: [a-z\\d]([a-z\\d-]*[a-z\\d])* => [a-z\\d]+(?:-+[a-z\\d]+)*.

Also, note you do not need to escape / chars, they are not special regex metacharacters, and you are not using a regex literal.

You may use

let validReg = new RegExp('^(https?://)?'+ // protocol '((([a-z\\d]+(?:-+[a-z\\d]+)*)\\.)+[a-z]{2,}|'+ // domain name '((\\d{1,3}\\.){3}\\d{1,3}))'+ // OR ip (v4) address '(:\\d+)?(/[-a-z\\d%_.~+]*)*'+ // port and path '(\\?[;&a-z\\d%_.~+=-]*)?'+ // query string '(#[-a-z\\d_]*)?$','i'); let isValid = validReg.test(component.repository_url);

@Travis This alone won't crash anything. What was the input string?
Actually you're right, I am unable to get it to crash now, so I must have made an error on my end. My apologies!

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