@coffeeandfun/maths-captcha/src/formatter.js

Maths-Captcha is a simple Node.js module that generates random math questions to verify human interaction. It creates math problems like addition, subtraction, multiplication, division, powers, percentages, sequences, and algebra, and checks if the user's

export function isValidNumericString(value) {
  if (typeof value !== 'string') return false;
  const trimmed = value.trim();
  if (trimmed === '') return false;
  if (!/^-?\d+(\.\d+)?$/.test(trimmed)) return false;
  return !Number.isNaN(Number(trimmed));
}

export function getDecimalPlaces(numericString) {
  const parts = numericString.split('.');
  return parts.length > 1 ? parts[1].length : 0;
}

export function isEffectivelyZero(numericString) {
  let sawDot = false;
  for (const char of numericString) {
    if (char === '-') continue;
    if (char === '.') {
      if (sawDot) return false;
      sawDot = true;
      continue;
    }
    if (char !== '0') return false;
  }
  return true;
}

export function numbersEqual(a, b, tolerance = 1e-10) {
  return Math.abs(a - b) < tolerance;
}

export function roundToDecimalPlaces(numericString, decimals) {
  const isNegative = numericString.startsWith('-');
  const absoluteString = isNegative ? numericString.slice(1) : numericString;

  let [integerPart, decimalPart = ''] = absoluteString.split('.');
  decimalPart = decimalPart.padEnd(decimals + 1, '0');

  const roundingDigit = parseInt(decimalPart[decimals] || '0', 10);
  let keptDecimals = decimalPart.slice(0, decimals);

  if (roundingDigit >= 5) {
    const carried = addOneToDecimalString(keptDecimals);
    if (carried.overflow) {
      integerPart = (BigInt(integerPart) + 1n).toString();
      keptDecimals = '0'.repeat(decimals);
    } else {
      keptDecimals = carried.result;
    }
  }

  const finalDecimals = keptDecimals.padEnd(decimals, '0');
  let result = decimals > 0 ? `${integerPart}.${finalDecimals}` : integerPart;

  if (isNegative && !isEffectivelyZero(result)) {
    result = `-${result}`;
  }
  return result;
}

export function normalizeNumericString(value) {
  const number = parseFloat(value);
  if (Number.isInteger(number)) return number.toString();
  return number.toString().replace(/\.?0+$/, '');
}

function addOneToDecimalString(decimalString) {
  if (!decimalString) return { result: '1', overflow: true };

  const digits = decimalString.split('').reverse();
  let carry = 1;

  for (let i = 0; i < digits.length && carry; i++) {
    const sum = parseInt(digits[i], 10) + carry;
    digits[i] = (sum % 10).toString();
    carry = Math.floor(sum / 10);
  }

  return {
    result: digits.reverse().join(''),
    overflow: carry > 0,
  };
}