Javascript Regex to avoid same character twice consecutively

Question

I need a regular expression to avoid having the same character(@ is the character) twice consecutively but can have them at muliple places. For example:

someword@someword is ok
someword@@someword is not ok
someword@someword@someword is ok too.

So basically this is my existing regular expression /^([a-zA-Z0-9'\-\x80-\xff\*\+ ]+),([a-zA-Z0-9'\-\x80-\xff\*\+\@ ]+)$/ where the first group is the last name and second group is the first name. I have introduced a magical character @ in the first name group which I will replace with a space when saving. The problem is I cannot have consecutive @ symbols.

and what have you tried?? – Psych Half Nov 06 '13 at 13:01 — Psych Half, Nov 06 '13 at 13:01

Reeno · Answer 1 · 2013-11-06T13:25:53.497

6

Looks for any repeated characters (repeated once):

/(.)\1/.test(string) // returns true if repeated characters are found

Looks for a repeated @:

string.indexOf('@@') !== -1 // returns true if @@ is found

edited Nov 06 '13 at 13:25

answered Nov 06 '13 at 13:04

Reeno

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This matches _any_ repeated character. I think the question is specifically about the @ character. You might want to address that in your answer. – Bryan Oakley Nov 06 '13 at 13:13
@Reeno sorry about that. I just wanted to explain more. – Vineeth Bolisetty Nov 06 '13 at 13:23

score 3 · Answer 2 · answered Nov 06 '13 at 13:11

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str.replace(/(@{2,})/g,'@')

works for any number of occorences.. @@, @@@, @@@@ etc

answered Nov 06 '13 at 13:11

TWL

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replace looks fine too. I can even look for consecutive @s at the back end too. But I wanted it in the regex as I have a particular set of characters allowed. – Vineeth Bolisetty Nov 06 '13 at 13:26

score 2 · Accepted Answer · answered Nov 06 '13 at 13:03

str.replace(/@@/g,'@')

finds and replaces all instances of '@@' by '@'. Also works if you have more than 2 consecutive '@' signs. Doesn't replace single @ signs or things that aren't @ signs.

edit: if you don't have to replace but just want to test on it:

/@@/.test(str)

Rajdeep Singh · Answer 4 · 2013-11-06T13:24:36.273

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Try this regex

/^(?!.*(.)\1)[a-zA-Z][a-zA-Z\d@]*$/

This regex will not allow @ consecutively

edited Nov 06 '13 at 13:24

answered Nov 06 '13 at 13:06

Rajdeep Singh

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This matches _any_ repeated character. I think the question is specifically about the @ character. You might want to address that in your answer. – Bryan Oakley Nov 06 '13 at 13:15
made the changes, have a look – Rajdeep Singh Nov 06 '13 at 13:26
@RajdeepSingh I tried again, it still doesn't allow _any_ successive characters – Nasta Jul 25 '22 at 14:03

score 0 · Answer 5 · answered Jul 25 '22 at 13:59

I didn't find any pure regex solution that worked for your use-case

So here is mine:

^([a-z0-9]@?)*[a-z0-9]$
 |____________|______|
       |          |-> Makes sure your string ends with an alphanumeric character
       |-> Makes sure the start of the string is a mix of single @ or alphanumeric characters
       |   It has to start with an alphanumeric character

Javascript Regex to avoid same character twice consecutively

5 Answers5