Home Why does using the RegEx /(?<=]),(?=(L|M|J|V))/gi with the JS split method give me this result?

Questions

Why does using the RegEx /(?<=]),(?=(L|M|J|V))/gi with the JS split method give me this result?

March 11, 2023

The title explains my problem. I don’t understand why using the RegEx /(?<=]),(L|M|J|V)/gi with the JS split() method on a string gives me an unexpected result.

Using said RegEx results in:

[
'Lunes[9:00-13:00,14:00-16:00]',
  'M',
  'Martes[19:00-3:00]',
  'M',
  'Miercoles[19:00-21:00,0:00-3:30]',
  'J',
  'Jueves[6:00-8:00,8:30-10:30,16:00-20:05]' 
]

instead of:

[
  'Lunes[9:00-13:00,14:00-16:00]',
  'Martes[19:00-3:00]',
  'Miercoles[19:00-21:00,0:00-3:30]',
  'Jueves[6:00-8:00,8:30-10:30,16:00-20:05]' 
]

My code:

    const pattern = /(?<=]),(?=(l|m|j|v))/gi;
    const myString = "Lunes[9:00-13:00,14:00-16:00],Martes[19:00-3:00],Miercoles[19:00-21:00,0:00-3:30],Jueves[6:00-8:00,8:30-10:30,16:00-20:05]";
    const myArray = myString.split(pattern);
    console.log(myArray);

>Solution :

It is due to the capture group in the lookahead, which you can omit
and use a character class instead of an alternation [lmjv]

const pattern = /(?<=]),(?=[lmjv])/gi;
const myString = "Lunes[9:00-13:00,14:00-16:00],Martes[19:00-3:00],Miercoles[19:00-21:00,0:00-3:30],Jueves[6:00-8:00,8:30-10:30,16:00-20:05]";
const myArray = myString.split(pattern);
console.log(myArray);