REGEXP.js

const punctuation = /^[~`!@#$%^&*(){}\[\];:"'<,.>?\/\\|_+=-]*$/g;
const letters = /^[^0-9~`!@#$%^&*(){}\[\];:"'<,.>?\/\\|_+=-]*$/g;
const usernamr = /^(?=.{8,20}$)(?![_.])(?!.*[_.]{2})[a-zA-Z0-9._]+(?<![_.])$/;

const replaceFirstTwoAndLastFour = (str, symbol) => {
  const re = /^(.{2})|(.{4})$/g
  return str.replace(re, replacer)

  function replacer(match) {
    return symbol.repeat(match.length)
  }
}

/*
https://stackoverflow.com/questions/12018245/regular-expression-to-validate-username
^(?=.{8,20}$)(?![_.])(?!.*[_.]{2})[a-zA-Z0-9._]+(?<![_.])$
 └─────┬────┘└───┬──┘└─────┬─────┘└─────┬─────┘ └───┬───┘
       │         │         │            │           no _ or . at the end
       │         │         │            │
       │         │         │            allowed characters, use \w – for Latin, numbers, underscore (eg usernames);
       │         │         │
       │         │         no __ or _. or ._ or .. inside
       │         │
       │         no _ or . at the beginning
       │
       username is 8-20 characters long
**/