Node.js solution

sc01.js

const fs = require("fs");
const puzzleInput = "172851-675869";
const RANGE = puzzleInput.split("-");
const LOWER = RANGE[0].length === 6 ? parseInt(RANGE[0]) : 0;
const HIGHER = RANGE[1].length === 6 ? parseInt(RANGE[1]) : 0;
if (!LOWER || !HIGHER) return;
let possiblePasswords = [];

if (fs.existsSync("./passwords.txt")) {
  fs.unlinkSync("./passwords.txt");
}

const checkAscending = (password) => {
  for (let index = 0; index < 5; index++) {
    if (password[index] > password[index + 1]) return false;
  }
  return true;
};

const checkAdjacent = (password) => {
  for (let index = 0; index < 5; index++) {
    const regex = new RegExp(`${password[index]}{2}`, "g");
    if (regex.test(password)) return true;
  }
  return false;
};

for (let number = LOWER; number <= HIGHER; number++) {
  if (checkAscending(number.toString())) {
    if (checkAdjacent(number.toString())) {
      possiblePasswords.push(number);
      fs.writeFileSync("passwords.txt", number + "\r\n", {
        encoding: "utf8",
        flag: "a+",
        mode: 0o666,
      });
    }
  }
}

const fulfills = possiblePasswords.length;
console.log("");
console.log(
  `There are ${fulfills} different passwords in range ${puzzleInput} meeting the criteria`
);
console.log("Se file: ./passwords.txt");
console.log("");