BigDecimal

bigDecimal.d.ts

export class BigDecimal {
  DECIMALS: number;
  ROUNDED: boolean;
  SHIFT: BigInt;
  _n: BigInt;
  constructor(value: number | string | BigDecimal | BigInt);
  static fromBigInt(bigint: BigInt): BigDecimal;
  add(num: number | string | BigDecimal | BigInt): BigDecimal;
  substract(num: number | string | BigDecimal | BigInt): BigDecimal;
  static _divRound(dividend: BigInt, divisor: BigInt): BigDecimal;
  multiply(num: number | string | BigDecimal | BigInt): BigDecimal;
  divide(num: number | string | BigDecimal | BigInt): BigDecimal;
  toString(): string;
  toLocaleString(): string;
}

bigDecimal.js

/**
 * Original source: https://stackoverflow.com/questions/16742578/bigdecimal-in-javascript
 * @author: trincot
 * @author: bigshans (Modified)
 * @example
 * var a = new BigDecimal("123456789123456789876");
 * var b = a.divide("10000000000000000000");
 * var c = b.add("9.000000000000000004");
 * console.log(b.toString());
 * console.log(c.toString());
 * console.log(c.toLocaleString());
 * console.log(+c); // loss of precision when converting to number
 */

export class BigDecimal {
  // Configuration: constants
  DECIMALS = 3; // number of decimals on all instances
  ROUNDED = true; // numbers are truncated (false) or rounded (true)
  SHIFT = BigInt("1" + "0".repeat(BigDecimal.DECIMALS)); // derived constant
  constructor(value) {
    if (value instanceof BigDecimal) {
      return value;
    }
    let [ints, decis] = String(value).split(".").concat("");
    this._n =
      BigInt(ints + decis.padEnd(this.DECIMALS, "0").slice(0, this.DECIMALS)) +
      BigInt(this.ROUNDED && decis[this.DECIMALS] >= "5");
  }
  static fromBigInt(bigint) {
    return Object.assign(Object.create(BigDecimal.prototype), { _n: bigint });
  }
  add(num) {
    return BigDecimal.fromBigInt(this._n + new BigDecimal(num)._n);
  }
  subtract(num) {
    return BigDecimal.fromBigInt(this._n - new BigDecimal(num)._n);
  }
  static _divRound(dividend, divisor) {
    return BigDecimal.fromBigInt(
      dividend / divisor +
        (this.ROUNDED ? ((dividend * 2n) / divisor) % 2n : 0n)
    );
  }
  multiply(num) {
    return BigDecimal._divRound(
      this._n * new BigDecimal(num)._n,
      BigDecimal.SHIFT
    );
  }
  divide(num) {
    return BigDecimal._divRound(this._n * this.SHIFT, new BigDecimal(num)._n);
  }
  toString() {
    const s = this._n.toString().padStart(this.DECIMALS + 1, "0");
    return s.slice(0, -this.DECIMALS) + "." + s.slice(-this.DECIMALS);
  }
  toLocaleString() {
    return this.toString().replace(/\d+/, function (n) {
      return n.replace(/(\d)(?=(\d{3})+$)/g, function ($1) {
        return $1 + ",";
      });
    });
  }
}