function replacer(key, value) {

  if(value instanceof Map) {

    return {

      dataType: 'Map',

      value: Array.from(value.entries()), // or with spread: value: [...value]

    };

  } else {

    return value;

  }

}

function reviver(key, value) {

  if(typeof value === 'object' && value !== null) {

    if (value.dataType === 'Map') {

      return new Map(value.value);

    }

  }

  return value;

}

const originalValue = new Map([['a', 1]]);

const str = JSON.stringify(originalValue, replacer);

const newValue = JSON.parse(str, reviver);

console.log(originalValue, newValue);