if (typeof BigInt !== 'undefined') {
  Object.defineProperties(BigInt.prototype, {
    abs: {
      value: function () {
        return this < 0n ? -this : this;
      },
      writable: true,
      enumerable: false,
      configurable: true,
    },
    sign: {
      value: function () {
        return this === 0n ? 0n : this < 0n ? -1n : 1n;
      },
      writable: true,
      enumerable: false,
      configurable: true,
    },
    pow: {
      value: function (exponent) {
        if (exponent < 0n) {
          throw new RangeError('Exponent must be non-negative');
        }
        if (exponent === 0n) {
          return 1n;
        }
        if (exponent === 1n) {
          return this;
        }
        let result = 1n;
        let base = this;
        while (exponent > 0n) {
          if (exponent % 2n === 1n) {
            result *= base;
          }
          base *= base;
          exponent /= 2n;
        }
        return result;
      },
      writable: true,
      enumerable: false,
      configurable: true,
    },
    sqrt: {
      value: function () {
        if (this < 0n) {
          throw new RangeError('Cannot calculate square root of a negative BigInt');
        }
        if (this < 2n) {
          return this;
        }
        const newtonStep = (n, x) => (x + n / x) >> 1n;
        const initialGuess = (this >> (BigInt(this.toString(16).length) - 1n)) + 1n;
        let x0 = initialGuess;
        let x1 = newtonStep(this, x0);
        while (x1 < x0) {
          x0 = x1;
          x1 = newtonStep(this, x0);
        }
        return x0;
      },
      writable: true,
      enumerable: false,
      configurable: true,
    },
    gcd: {
      value: function (other) {
        if (typeof other !== 'bigint') {
          throw new TypeError('Argument must be a BigInt');
        }
        let a = this.abs();
        let b = other.abs();
        if (b === 0n) {
          return a;
        }
        let r;
        while ((r = a % b) !== 0n) {
          a = b;
          b = r;
        }
        return b;
      },
      writable: true,
      enumerable: false,
      configurable: true,
    },
    lcm: {
      value: function (other) {
        if (typeof other !== 'bigint') {
          throw new TypeError('Argument must be a BigInt');
        }
        if (this === 0n || other === 0n) {
          return 0n;
        }
        return (this / this.gcd(other)) * other;
      },
      writable: true,
      enumerable: false,
      configurable: true,
    },
  });
}
// 使用例
if (typeof BigInt !== 'undefined') {
  const bigIntValue = -123n;
  console.log(bigIntValue.abs()); // 123n
  console.log(bigIntValue.sign()); // -1n
  console.log(2n.pow(10n)); // 1024n
  console.log(25n.sqrt()); // 5n
  console.log(26n.sqrt()); // 5n
  console.log(12n.gcd(18n)); // 6n
  console.log(12n.lcm(18n)); // 36n
}