Simple script to match `an+b` type expressions

anb.js

/**
 * @param {number} value
 * @param {string} pattern
 */
function matchesAnB(value, pattern) {
  let a = 1, b = pattern;
  if (pattern.includes('n')) {
    [a, b] = pattern.split('n', 2);
  }
  let result = (value - (b || 0)) / (a || 1);
  return /* value >= 0 && */ result >= 0 && Number.isInteger(result);
}

for (const [value, pattern] of [
  [2, '2'],
  [3, '2'],
  [-2, '2'],
  [2, 'n'],
  [2, 'n+1'],
  [2, 'n+2'],
  [2, 'n+3'],
  [3, 'n+3'],
  [0, '2n+2'],
  [2, '2n+2'],
  [3, '2n+2'],
  [4, '2n+2'],
  [6, '-2n+4'],
  [4, '-2n+4'],
  [2, '-2n+4'],
  [0, '-2n+4'],
]) {
  console.log(`${value} matches ${pattern}`, matchesAnB(value, pattern));
}