When the judge of the municipal court or the justice of the peace in any city having only 1 municipal judge or justice of the peace, who is paid a salary in lieu of fees, is unable to perform the duties of his office by reason of illness or absence from the city, said judge, justice of the peace, or his chief clerk may designate any other justice of the peace or municipal judge of the same county to sit in the court of the municipal judge or justice of the peace who is absent or ill: Provided, That no justice of the peace or municipal judge shall be so designated unless qualified under the provisions of the city charter. The judge or justice of the peace so designated shall perform the duties and exercise all of the powers of the municipal judge or justice of the peace in whose court he is sitting during such absence or illness and his compensation shall be in the same amount and payable from the same fund as that paid to such absent or incapacitated judge.