How to write regex for domain validation that will trigger pattern error in Angular form

Question

I am validating a domain field in the form. I am using Validators.pattern(this.domainPattern) for doing that. I am using below pattern:

public domainPattern: string = "^(?:[a-z0-9][a-z0-9-]{0,61}[a-z0-9]\.)+[a-z0-9][a-z0-9-]{0,61}[a-z0-9]$";

It works fine for many cases. But when there is a white space in domain it is not triggering pattern error. What I am missing?

Quick help will be highly appreciated.

Thanks.

Answer 1

Try this pattern:

(?(?<= )(?=[^ ])|^)(?:[a-z0-9][a-z0-9-]{0,61}[a-z0-9]\.)+[a-z0-9][a-z0-9-]{0,61}[a-z0-9]

I just added (?(?<= )(?=[^ ])|^) , conditional which checks:

first it checks condition (?<= ) if what is preceeding is space, if it is, then check if what's after is not a space with (?=[^ ]) , if the condition fails, then check if we are at the beginning of a string with ^ .

Demo

UPDATE

OP said:

I want user to enter just one valid domain name. If user enters "google.com google.com" it should be treated as invalid

Then you could use this pattern

^(?!.* .*)(?:[a-z0-9][a-z0-9-]{0,61}[a-z0-9]\.)+[a-z0-9][a-z0-9-]{0,61}[a-z0-9]$

Just added (?!.* .*) which checks if there's sapce in following line, if it is, then it won't match anything, as space indicated multiple domain names.

Another demo