BigInt Base62 Encoding

base62-bigint.ts

import * as assert from 'assert';

/**
 * https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/BigInt
 */
export class Base62 {
  private readonly base: bigint = BigInt(62);
  private readonly charset: string[] = '0123456789abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ'.split('');

  public encode(integer: string): string {
    if (Number(integer) === 0) {
      return '0';
    }

    let num: bigint = BigInt(integer);
    let str: string[] = [];

    while (num > 0) {
      str = [this.charset[num % this.base], ...str];
      num = num / this.base;
    }

    return str.join('');
  }

  public decode(str: string): string {
    return str.split('').reverse().reduce(
      (prev: bigint, char: string, i: number) =>
        prev + (BigInt(this.charset.indexOf(char)) * (this.base ** BigInt(i))),
      BigInt(0)).toString();
  }
}

export const base62: Base62 = new Base62();

// Test
const numbers: string[] = [
  '0', '1', '2', '3', '4', '5', '1234567890', '9876543210',
  '616580508813361172', '616580508813361200', '793548328091516928',
  '24809234902840923840294829048204', '90275980235738905734980573490857'];
for (const numstr of numbers) {
  const encode: string = base62.encode(numstr);
  console.log(numstr, encode);

  assert.strictEqual(numstr, base62.decode(encode));
}