Removing subdomain in a string in TypeScript

Question

I have a string in TypeScript which is subdomain.domain.com I want to create a new string that is just the domain on its own, so for example subdomain.domain.com would become domain.com

Note: The 'subdomain' part of the URL could be different sizes so it could be 'subdomain.domain.com' or it might be 'sub.domain.com' so I can't do this on character size. The domain might also be different so it could be 'subdomain.domain.com' or it could be 'subdomain.new-domain.com'.

So basically I need to just remove up to and including the first '.' - hope that all makes sense.

Does this answer your question? How to remove part of a string before a ":" in javascript? (just replace ":" with ".") — Heretic Monkey
– Heretic Monkey, Commented Aug 4, 2021 at 15:13
No because I noticed there was a note that if there's multiple ':' in the string it will only work on the last one it encounters - with this being a domain name it has the three '.' in it so I'm worried that solution won't work — Web Develop Wolf
– Web Develop Wolf, Commented Aug 4, 2021 at 15:15
There are three solutions presented in the answer. Did you try any of them? The warning is only for the second of the three. — Heretic Monkey
– Heretic Monkey, Commented Aug 4, 2021 at 15:18
What did you try so far ? did you try using regex for example ? — Wahalez
– Wahalez, Commented Aug 4, 2021 at 15:19
There is also Remove part of the string before the FIRST dot with js or Get domain name without subdomains using JavaScript? — Heretic Monkey
– Heretic Monkey, Commented Aug 4, 2021 at 15:28

Praveen Thirumurugan · Accepted Answer · 2021-08-04 15:34:12Z

0

var domain = 'mail.testing.praveent.com';

var domainCharacters = domain.split('').reverse();
var domainReversed = '', dotCount = 0;

do {
    if (domainCharacters[0] === '.') {
        dotCount++;
        if (dotCount == 2) break;
    }
    domainReversed += domainCharacters[0];
    domainCharacters.splice(0, 1);
} while (dotCount < 2 && domainCharacters.length > 0);

var domainWithoutSubdomain = domainReversed.split('').reverse().join('');

This will strip off the subdomains in a domain and give the root (@) domain name alone.

answered Aug 4, 2021 at 15:34

Praveen Thirumurugan

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2 Comments

Dhruv Thakkar Over a year ago

This won't work from urls like mail.testing.praveent.co.uk

Praveen Thirumurugan Over a year ago

Nice catch. In this case, we would need to save a map of all TLDs and check against them to find the number of dot chains to filter.

John Michael Manlupig · Accepted Answer · 2021-08-04 15:42:57Z

-1

You can split it by . and get only the last 2 elements and turn it back into a string again.

function strip(url: string) {
    const fragments = url.split('.');
    const last = fragments.pop();
    try {
        // if its a valid url with a protocol (http/https)
        const instance = new URL(url);
        return `${instance.protocol}//${fragments.pop()}.${last}`;
    } catch (_) {
        return `${fragments.pop()}.${last}`;
    }
}

strip('https://subdomain.example.com') // https://example.com
strip('subdomain.example.com') // example.com
strip('https://subdomain.another-subdomain.example.com') // https://example.com

edited Aug 4, 2021 at 15:42

answered Aug 4, 2021 at 15:28

John Michael Manlupig

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4 Comments

Praveen Thirumurugan Over a year ago

This will not strip off multiple sub-domains in a single string.

John Michael Manlupig Over a year ago

You're right, I didn't know multiple sub-domains was possible up until now. But it does work if it's not multiple sub-domains.

Praveen Thirumurugan Over a year ago

Also, try with subdomain-demo-example.com. This is a valid domain but the function returns just com as response.

John Michael Manlupig Over a year ago

I edited the answer. Hope I got it right.

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