Checking url is duplicate in textfield

Question

I had a text field and we can copy and paste url on it. Sometimes user are pasting the url twice like

"http://www.google.com/test/index.htmlhttp://www.google.com/test/index.html".

How can i find out that url is duplicated.

I tried using below code

var url="http://www.google.com/test/index.htmlhttp://www.google.com/test/index.html";

var exp =/https?:\/\//gi;

alert(url.match(exp).length);

If length is greater than 1 then it is duplicate. Trying for the any best option to find duplicate.

Well, you won't really know whether it is a duplicate, just that there are two urls in there — Stultuske, Sep 02 '15 at 07:18
It seems to be enough. If you plan to really match duplicated URLs, just use [`^(https?:\/\/\S+?)\1+$`](https://regex101.com/r/iN6kF5/2). Though I believe what you have in your case is really sufficient to check for a malformed URL containing more than 1 protocol. — Wiktor Stribiżew, Sep 02 '15 at 07:21
I suspect the question is a dupe of [What is the best regular expression to check if a string is a valid URL?](http://stackoverflow.com/questions/161738/what-is-the-best-regular-expression-to-check-if-a-string-is-a-valid-url) — Wiktor Stribiżew, Sep 02 '15 at 07:30
if the case is as specific as described, `url.substr(0, url.length/2)===url.substr(url.length/2)` would be enough. — Serge Seredenko, Sep 02 '15 at 07:34
Does this code at http://jsfiddle.net/t6zL18qL/1/ works for you? — Wiktor Stribiżew, Sep 02 '15 at 09:12

score 0 · Answer 1 · answered Sep 02 '15 at 07:24

0

I suggest using a better regex. You do not need to check for each possible problem separately, if the user input does not match the regex then it is not valid. Try the following:

^(https?:\/\/)?([\da-z\.-]+)\.([a-z\.]{2,6})([\/\w \.-]*)*\/?$

answered Sep 02 '15 at 07:24

dchar

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score 0 · Answer 2 · edited May 23 '17 at 11:44

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If client always paste url with http: prefix simply count the ':' occurrence in String. If its more than one you will know that it has wrong format.

Some helper of counting chars in Java: How do I count the number of occurrences of a char in a String?

edited May 23 '17 at 11:44

Community

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answered Sep 02 '15 at 07:28

graczun

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Some times url may be like www.google.com with out protocol(like http/https:) then i need to add the protocol. – CNKR Sep 02 '15 at 07:35
so client can paste something like www.google.comwww.google.com and AFAIK it could be valid URL (strange, but compatible with URL semantics). You can always count 'www.' and if it has more than 1 occurence throw exceptions. But it wouldn't work in all scenarios ( for example www.comwww.com). In this case I would not consider my answer as valid one. – graczun Sep 02 '15 at 07:44
@user3498863: Do not add details in the comments for an answer, you should update the question. In case you are *sure* the pasted string is URL and you need to use [something like this](http://jsfiddle.net/t6zL18qL/1/). Please let me know if it works for you, I will post then. – Wiktor Stribiżew Sep 02 '15 at 07:58

score 0 · Answer 3 · answered Sep 02 '15 at 07:54

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If you're just trying to detect someone double pasting, you can use string.length and string.substring to detect the duplicate, eg:

if (url.length % 2 === 0 && url.substring(0, url.length/2) === url.substring(url.length/2, url.length/2)) {
    alert('Dupe');
}

That said, if you're trying to detect duplicates that also match a pattern, I guess you can use pattern capture groups and backreferences, like:

/^(https?:\/\/.*)\1$/

answered Sep 02 '15 at 07:54

Jon Marnock

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The problem will arise if the URL is tripled, or quadrupled. Also, OP says the URL can start with no protocol at all. – Wiktor Stribiżew Sep 02 '15 at 07:59
Yep, OP didn't mention triples etc, just occasional doubling. If it needs to detect arbitrary repeats, regex is ~definitely~ not the right way to go. Re being able to deal with no protocol at all, that's fine - the part inside the brackets was just meant to be a placeholder which OP can replace with whatever regex they prefer to match a valid URL. (I specifically copied the regex OP provided in their question) – Jon Marnock Sep 02 '15 at 08:01

score 0 · Accepted Answer · answered Sep 02 '15 at 10:18

I sugges using /^(\S+)\1+$/ to match any characters from the beginning of the string with (\S+), and then use \1+ backreference to see if the sequence is duplicated, or tripled, or quadrupled (+ makes this repetition possible).

Thus, you can use

function sanitizeUrl(urls) {
    var uniq = urls.match(/^(\S+)\1+$/);
    if (uniq !== null) {
       return uniq[1].substring(0, 4) !== "http" ? "http://" + uniq[1] : uniq[1];
    }
}

var urls = "google.com/test/index.htmlgoogle.com/test/index.html"; // No HTTP
document.getElementById("r").innerHTML = sanitizeUrl(urls) + "<br/>";
urls = "http://www.google.com/test/index.htmlhttp://www.google.com/test/index.htmlhttp://www.google.com/test/index.html";
document.getElementById("r").innerHTML += sanitizeUrl(urls);

<div id="r"/>

The uniq[1].substring(0, 4) !== "http" ? "http://" + uniq[1] : uniq[1] logic either adds http:// or not depending on the result obtained.

Glad it worked for you. Please also consider upvoting if my answer proved helpful to you. [See How to upvote on Stack Overflow?](http://meta.stackexchange.com/questions/173399/how-to-upvote-on-stack-overflow) — Wiktor Stribiżew, Sep 02 '15 at 10:21

Checking url is duplicate in textfield

4 Answers4