Javascript regex - check if string contains two or more of same letter

Question

I'm working on some regex with JavaScript. I have now created a regex that checks if a string has two or more of the same letter following each other. I would want to create a regex that checks if a word / string contains two or more of one particular letter, no matter if they are after each other or just in the same word / string.

It would need to match: drama and anaconda, but not match: lame, kiwi or tree.

This is the regex in JS.

const str = "anaconda"; 
str.match(/[a]{2,}/);

Maybe all you need is /a.*a/ (or /a[^a]*a/) to test if a string contains at least two as? — Wiktor Stribiżew
– Wiktor Stribiżew, Commented Feb 11, 2021 at 20:22

Ryszard Czech · Accepted Answer · 2021-02-11 22:56:23Z

2

Use

\w*(\w)\w*\1\w*

See proof

EXPLANATION

NODE                     EXPLANATION
--------------------------------------------------------------------------------
  \w*                      word characters (a-z, A-Z, 0-9, _) (0 or
                           more times (matching the most amount
                           possible))
--------------------------------------------------------------------------------
  (                        group and capture to \1:
--------------------------------------------------------------------------------
    \w                       word characters (a-z, A-Z, 0-9, _)
--------------------------------------------------------------------------------
  )                        end of \1
--------------------------------------------------------------------------------
  \w*                      word characters (a-z, A-Z, 0-9, _) (0 or
                           more times (matching the most amount
                           possible))
--------------------------------------------------------------------------------
  \1                       what was matched by capture \1
--------------------------------------------------------------------------------
  \w*                      word characters (a-z, A-Z, 0-9, _) (0 or
                           more times (matching the most amount
                           possible))

answered Feb 11, 2021 at 22:56

Ryszard Czech

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4 Comments

The fourth bird Over a year ago

Yes for word characters I think this would be it.

Krullmizter Over a year ago

Thanks for the answer, with great explanation! But in this case the regex would match for example the word: tree and kiwi, and I only want the match to happen if the word in question has two or more: As in the given string. Any input on this issue?

Krullmizter Over a year ago

Could this be a solution: [a]*([a])\w*\1[a]* ?

Ryszard Czech Over a year ago

@Krullmizter Not quite.

shubhushan shambhu · Accepted Answer · 2021-02-11 22:33:27Z

0

My thought process was something like this:

A word can start with any Alphabet
A word can end with any Alphabet
Similar letters can have zero or multiple alphabets between them
If any of it's letters are similar and it fits the criteria above then accept the word

     regex = /[a-z]*([a-z])[a-z]*\1+[a-z]*/

answered Feb 11, 2021 at 22:33

shubhushan shambhu

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