javascript regex detect duplicate blank lines

I tried to detect duplicate blank lines with

\s*\n\n+

https://regex101.com/r/v0imUZ/1

but doesn’t seem to work with

  test1
   
    
   
   test2
   test3
  test4

  test1
   
    
   
   test2
   test3
  test4

>Solution :

You can use

\n(?:[^\S\n]*\n)+

See the regex demo. If there can be CRLF endings:

\r?\n(?:[^\S\n\r]*\r?\n)+

Details:

• \r? – an optional carriage return symbol
• \n – a newline char
• (?:[^\S\n]*\n)+ – one or more occurrences of
  • [^\S\n]* – zero or more whitespace chars excluding newline char, and then
  • \n – a newline char.