Regex for repeating pattern

Question

I need a regex which satisfies the following conditions. 1. Total length of string 300 characters. 2. Should start with &,-,/,# only followed by 3 or 4 alphanumeric characters 3. This above pattern can be in continuous string upto 300 characters

String example - &ACK2-ASD3#RERT...

I have tried repeating the group but unsuccessful.

(^[&//-#][A-Za-z0-9]{3,4})+ 

That is not working ..just matches the first set

Answer 1

You may validate the string first using /^(?:[&\/#-][A-Za-z0-9]{3,4})+$/ regex and checking the string length (using s.length <= 300) and then return all matches with a part of the validation regex:

var s = "&ACK2-ASD3#RERT";
var val_rx = /^(?:[&\/#-][A-Za-z0-9]{3,4})+$/;
if (val_rx.test(s) && s.length <= 300) {
  console.log(s.match(/[&\/#-][A-Za-z0-9]{3,4}/g));
}

Regex details

• ^ - start of string
• (?:[&\/#-][A-Za-z0-9]{3,4})+ - 1 or more occurrences of:
  • [&\/#-] - &, /, # or -
  • [A-Za-z0-9]{3,4} - three or four alphanumeric chars
• $ - end of string.

See the regex demo.

Note the absence of g modifier with the validation regex used with RegExp#test and it must be present in the extraction regex (as we need to check the string only once, but extract multiple occurrences).