It works. If is the best way, I do not know. :D

doMask.test.ts

import { doMask, moneyMask } from "@common/utils/doMask";

describe('doMask', () => {
  it('should correctly apply a basic mask (left-to-right)', () => {
    const result = doMask('123456', '#-#-#');
    expect(result).toBe('1-2-3');
  });

  it('should correctly handle an empty value', () => {
    const result = doMask('', '#-#-#');
    expect(result).toBe('');
  });

  it('should correctly handle an empty pattern', () => {
    const result = doMask('123456', '');
    expect(result).toBe('');
  });

  it('should correctly apply a mask with special characters', () => {
    const result = doMask('123456', '###.###');
    expect(result).toBe('123.456');
  });

  it('should stop applying the mask when the value is fully consumed', () => {
    const result = doMask('123', '###.###');
    expect(result).toBe('123');
  });

  it('should apply a reversed mask correctly', () => {
    const result = doMask('1234', '###.###', { reverse: true });
    expect(result).toBe('1.234');
  });

  it('should apply a custom character pattern', () => {
    const result = doMask('ABCDEF', '**-**', { charPattern: '*' });
    expect(result).toBe('AB-CD');
  });

  it('should correctly handle a value shorter than the mask length', () => {
    const result = doMask('12', '###.###.###');
    expect(result).toBe('12');
  });

  it('should correctly handle a reversed mask with shorter value', () => {
    const result = doMask('12', '###.###', { reverse: true });
    expect(result).toBe('12');
  });
});

describe('moneyMask', () => {
  it('should format a value into a money mask pattern', () => {
    const result = moneyMask('123456');
    expect(result).toBe('1.234,56');
  });

  it('should handle an empty value gracefully', () => {
    const result = moneyMask('');
    expect(result).toBe('');
  });

  it('should handle a value shorter than the money mask pattern', () => {
    const result = moneyMask('12');
    expect(result).toBe('0,12');
  });

  it('should handle non-numeric input gracefully', () => {
    const result = moneyMask('abcd');
    expect(result).toBe('');
  });
});

doMask.ts

/**
This write from left to right
 Patterns example: 
    +## # ## ####-####
    ###.###.###-##
    ##############
    (##) # ####-####
*/

  
type maskPatterProp = {
  reverse?: boolean;
  charPattern?: string;
};

export const doMask = (
  value: string,
  pattern: string,
  opt: maskPatterProp = { reverse: false, charPattern: "#" },
): string => {
  const { reverse = false, charPattern = "#" } = opt;
  const patternArray = reverse
    ? pattern.split("").reverse()
    : pattern.split("");
  const valueArray = reverse ? value.split("").reverse() : value.split("");
  const limitIndexPattern = patternArray.length;

  let resultMask = "";
  let indexValue = 0;
  for (let indexPattern = 0; indexPattern < limitIndexPattern; indexPattern++) {
    const pat = patternArray[indexPattern];

    if (indexValue >= valueArray.length) {
      break;
    }

    if (pat === charPattern) {
      if (valueArray[indexValue]) {
        resultMask = `${resultMask}${valueArray[indexValue]}`;
        indexValue++;
      }
    } else {
      resultMask = `${resultMask}${pat}`;
    }
  }

  return reverse ? resultMask.split("").reverse().join("") : resultMask;
};