Develop Reference

Why would the replace with regex not work even though the regex does?

There may be a very simple answer to this, probably because of my familiarity (or possibly lack thereof) of the replace method and how it works with regex.
Let's say I have the following string: abcdefHellowxyz
I just want to strip the first six characters and the last four, to return Hello, using regex... Yes, I know there may be other ways, but I'm trying to explore the boundaries of what these methods are capable of doing...
Anyway, I've tinkered on http://regex101.com and got the following Regex worked out:
/^(.{6}).+(.{4})$/
Which seems to pass the string well and shows that abcdef is captured as group 1, and wxyz captured as group 2. But when I try to run the following:
"abcdefHellowxyz".replace(/^(.{6}).+(.{4})$/,"")
to replace those captured groups with "" I receive an empty string as my final output... Am I doing something wrong with this syntax? And if so, how does one correct it, keeping my original stance on wanting to use Regex in this manner...
Thanks so much everyone in advance...

The code below works well as you wish
"abcdefHellowxyz".replace(/^.{6}(.+).{4}$/,"$1")
I think that only use ()to capture the text you want, and in the second parameter of replace(), you can use $1 $2 ... to represent the group1 group2.
Also you can pass a function to the second parameter of replace,and transform the captured text to whatever you want in this function.
For more detail, as #Akxe recommend , you can find document on https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/String/replace.

You are replacing any substring that matches /^(.{6}).+(.{4})$/, with this line of code:
"abcdefHellowxyz".replace(/^(.{6}).+(.{4})$/,"")
The regex matches the whole string "abcdefHellowxyz"; thus, the whole string is replaced. Instead, if you are strictly stripping by the lengths of the extraneous substrings, you could simply use substring or substr.
Edit
The answer you're probably looking for is capturing the middle token, instead of the outer ones:
var str = "abcdefHellowxyz";
var matches = str.match(/^.{6}(.+).{4}$/);
str = matches[1]; // index 0 is entire match
console.log(str);

Check if valid steam profile url

I am trying to make a regex that checks if the url a user is posting, are valid.
I have created the following regex:
/https?\:\/steamcommunity\/.com\/profiles|id\/[a-zA-Z0-9]/
But that isn't working. Is there a regex master, here that can tell me what i am doing wrong?
The links i am trying to validate are looking like:
https://steamcommunity.com/profiles/76561198009610232/
https://steamcommunity.com/id/rasmusvejby/
ANSWERE
/(?:https?:\/\/)?steamcommunity\.com\/(?:profiles|id)\/[a-zA-Z0-9]+/

Try this regex:
(?:https?:\/\/)?steamcommunity\.com\/(?:profiles|id)\/[a-zA-Z0-9]+
See this demo:
Regex Demo
The "g" modifier is just so you can see it test it in different strings, but you probably dont need it.

The accepted answer to this question will also match this url for example:
https://steamcommunity.com/profile/thisisimpossible
I am using the following regex to prevent non numeric characters when the id is prepended by profile/ rather than id/. Not necessarily prettier but it does the job.
^(?:https?:\/\/)?steamcommunity\.com\/(?:profiles\/[0-9]{17}|id\/[a-zA-Z0-9].*)$

Bookmarklet - Verify URL format and extract substring

I'm trying to build a bookmarklet that preforms a service client side, but I'm not really fluent in Javascript. In my code below I want to take the current page url and first verify that it's a url following a specific format after the domain, which is...
/photos/[any alphanumeric string]/[any numeric string]
after that 3rd "/" should always be the numeric string that I need to extract into a var. Also, I can't just start from the end and work backwards because there will be times that there is another "/" after the numeric string followed by other things I don't need.
Is indexOf() the right function to verify if the url is the specific format and how would I write that expression? I've tried several things related to indexOf() and Regex(), but had no success. I seem to always end up with an unexpected character or it just doesn't work.
And of course the second part of my question is once I know the url is the right format, how do I extract the numeric string into a variable?
Thank you for any help!
javascript:(function(){
// Retrieve the url of the current page
var photoUrl = window.location.pathname;
if(photoUrl.indexOf(/photos/[any alphanumeric string]/[any numeric string]) == true) {
// Extract the numeric substring into a var and do something with it
} else {
// Do something else
}
})();

var id = window.location.pathname.match(/\/photos\/(\w+)\/(\d+)/i);
if (id) alert(id[1]); // use 1 or 2 depending on what you want
else alert('url did not fit expected format');
(EDIT: changed first \d* to \w+ and second \d* to \d+ and dig to id.)

To test strings for patterns and get their parts, you can use regular expressions. Exression for your criteria would be like this:
/^\/photos\/\w+\/(\d+)\/?$/
It will match any string starting with /photos/, followed by any alphanumeric character (and underscore), followed by any number and optional / at the end of string, wrapped in a capture group.
So, if we do this:
"/photos/abc123/123".match(/^\/photos\/\w+\/(\d+)\/?$/)
the result will be ["/photos/abc123/123", "123"]. As you might have noticed, capture group is the second array element.
Ready to use function:
var extractNumeric = function (string) {
var exp = /^\/photos\/\w+\/(\d+)\/?$/,
out = string.match(exp);
return out ? out[1] : false;
};
You can find more detailed example here.
So, the answers:
Is indexOf() the right function to verify if the url is the specific
format and how would I write that expression? I've tried several
things related to indexOf() and Regex(), but had no success. I seem to
always end up with an unexpected character or it just doesn't work.
indexOf isn't the best choice for the job, you were right about using regular expression, but lacked experience to do so.
And of course the second part of my question is once I know the url is
the right format, how do I extract the numeric string into a variable?
Regular expression together with match function will allow to test string for desired format and get it's portions at the same time.

How to use a javascript Regex to globally find and replace the beginning of a string from a textarea

I am trying to replace any non encoded ampersands in a string in JavaScript and was wondering if this was possible. I have the regex build to detect this in the string, but when I do a replace, I will lose the parameter name.
Current input:
http://www.somesite.com/id/2343?paramA=1&paramB=asdf
From a textarea
<textarea id='test-box'>http://www.somesite.com/id/2343?paramA=1&paramB=asdf</textarea>
var str = $('#test-box').val();;
var regex = /&[a-z]+=/gi;
str = str.replace(regex, [REPLACE &'s WITH &'s]);
console.log(str);
Desired output:
http://www.somesite.com/id/2343?paramA=1&paramB=asdf
How can I then use JavaScript to keep the name of the parameter and simply replace the '&' with '&'?

Try this regex: /&(?=[a-z]+=)/ and this replacement: &
This uses a lookahead assertion rather than eating up the parameter name.

If you have a URL which might be partially encoded in HTML, and you're trying to make a best effort at producing XHTML validating textarea content, then you can use the list of HTML character references to identify ampersands which are not part of an HTML character reference:
str.replace(/&(?!#(?:[0-9]|[xX][0-9A-Fa-f])|lt;|gt;|amp|...)/g, '&')
where ... is replaced with the set of entities from that list that you care to recognize.
Note that most of those character references end in semicolon, so are not allowed to be followed immediately by an equals sign, so are not ambiguous with URL parameters. Only certain entities can appear without a semicolon for backwards compatibility.
If you don't care about validating, then you can just let the browser take care of it by ensuring that your URL doesn't contain the substring </textarea by doing something like
str.replace(/</g, '%3c')

Apart from lookahead assert, you can also use a backreference:
var regex = /&([a-z]+)=/gi;
str = str.replace(/&([a-z]+)=/gi,'&$1');
When $n appears in the replace string, it will be replaced by the n'th parenthesized pattern in the regexp.

Who needs regex when you've got jQuery html(). Especially since you've got a jquery tag on your question :D
What this does is leverage the browser's innerHTML property. see api
Fiddle
var str = 'http://www.somesite.com/id/2343?paramA=1&paramB=asd';
$('#test-box').text(str);
$('#html-box').text($('#test-box').html());

Regular expression for browser Url

I am new to JavaScript
i need a regular expression which
allows both of this forms
for example :
http://www.google.com
www.google.com

var url_pattern = new RegExp("((ftp|http|https)(:\/\/))?([a-zA-Z0-9]+[.]{1}){2}[a-zA-z0-9]+(\/{1}[a-zA-Z0-9]+)*\/?", "i");
return url_pattern.test(url);

(ftp|http|https):\/\/(\w+:{0,1}\w*#)?(\S+)(:[0-9]+)?(\/|\/([\w#!:.?+=&%#!\-\/]))?
This works quite well.

I've just written up a blog post on recognising URLs in most used formats such as:
www.google.com
http://www.google.com
mailto:somebody#google.com
somebody#google.com
www.url-with-querystring.com/?url=has-querystring
The regular expression used is /((([A-Za-z]{3,9}:(?:\/\/)?)(?:[-;:&=\+\$,\w]+#)?[A-Za-z0-9.-]+|(?:www.|[-;:&=\+\$,\w]+#)[A-Za-z0-9.-]+)((?:\/[\+~%\/.\w-_]*)?\??(?:[-\+=&;%#.\w_]*)#?(?:[\w]*))?)/ however I would recommend you got to http://blog.mattheworiordan.com/post/13174566389/url-regular-expression-for-links-with-or-without-the to see a complete working example along with an explanation of the regular expression in case you need to extend or tweak it.

^((?:(?:https?|ftp):)?\/\/?)?(?:\S+(?::\S*)?#)?(?:(?!10(?:\.\d{1,3}){3})(?!127(?:\.\d{1,3}){3})(?!169\.254(?:\.\d{1,3}){2})(?!192\.168(?:\.\d{1,3}){2})(?!172\.(?:1[6-9]|2\d|3[0-1])(?:\.\d{1,3}){2})(?:[1-9]\d?|1\d\d|2[01]\d|22[0-3])(?:\.(?:1?\d{1,2}|2[0-4]\d|25[0-5])){2}(?:\.(?:[1-9]\d?|1\d\d|2[0-4]\d|25[0-4]))|(?:(?:[a-z\x{00a1}-\x{ffff}0-9]+-?)*[a-z\x{00a1}-\x{ffff}0-9]+)(?:\.(?:[a-z\x{00a1}-\x{ffff}0-9]+-?)*[a-z\x{00a1}-\x{ffff}0-9]+)*(?:\.(?:[a-z\x{00a1}-\x{ffff}]{2,})))(?::\d{2,5})?(?:\/[^\s]*)?$
Test it! https://regex101.com/r/qQ8uV6/1
Extracted from In search of the perfect URL validation regex https://mathiasbynens.be/demo/url-regex (modified it a bit).
credits to #diegoperini.
If you test it in JavaScript, you'll get a nice
ParseError: Error parsing regular expression: Invalid regular expression
....
Range out of order in character class
You need to replace \x{xxxx} for \uxxxx. So in JavaScript it'll be:
^(?:(?:https?|ftp):\/\/)?(?:\S+(?::\S*)?#)?(?:(?!10(?:\.\d{1,3}){3})(?!127(?:\.\d{1,3}){3})(?!169\.254(?:\.\d{1,3}){2})(?!192\.168(?:\.\d{1,3}){2})(?!172\.(?:1[6-9]|2\d|3[0-1])(?:\.\d{1,3}){2})(?:[1-9]\d?|1\d\d|2[01]\d|22[0-3])(?:\.(?:1?\d{1,2}|2[0-4]\d|25[0-5])){2}(?:\.(?:[1-9]\d?|1\d\d|2[0-4]\d|25[0-4]))|(?:(?:[a-z\u00a1-\ufff0-9]+-?)*[a-z\u00a1-\uffff0-9]+)(?:\.(?:[a-z\u00a1-\uffff0-9]+-?)*[a-z\u00a1-\uffff0-9]+)*(?:\.(?:[a-z\u00a1-\uffff]{2,})))(?::\d{2,5})?(?:\/[^\s]*)?$
Just like stated in JavaScript Unicode Regex - Range out of order in character class