a functional appropach

solution-functional.js

function getNumber() {
  return Math.floor(Math.random() * 10000);
}

function getFourDigitNum(pin) {
  if (pin <= 1000) {
    getFourDigitNum(getNumber());
  }

  return pin;
}

function getStuffInShape(pin) {
  const stringArr = pin.toString().split('');
  const stringSet = new Set(stringArr);

  const numArr = stringArr.map(item=>parseInt(item));
  const isValid =
    numArr[1] - numArr[0] !== 1 &&
    numArr[2] - numArr[1] !== 1 &&
    numArr[3] - numArr[2] !== 1;

  if (stringSet.size === 4 && isValid) {
    return pin;
  }

  return getStuffInShape(
    getFourDigitNum(getNumber())
  );
}

function getSolution(howMany) {
  const result = new Set();
  return function getEach(pin) {
    if (typeof pin === 'undefined') {
      console.log('error!');
    }
    result.add(pin);
    if (result.size !== howMany) {
      getEach(
        getStuffInShape(
          getFourDigitNum(getNumber())
        )
      );
    }
    return result;
  };
}

// console.log(
//   Array.from(
//     getSolution(1000)(
//       getStuffInShape(
//         getFourDigitNum(getNumber())
//       )
//     )
//   ).join(',')
// );

module.exports = getSolution(1000);