How do we create a new log file every week using log4js

Question

Following code doesn't work it prints ww instead of week number, same in case of pattern yyyy-MM-ww

const log4js = require('log4js');

log4js.configure({
  appenders: {
    weekly: {
      type: 'dateFile',
      filename: 'logs/app.log',
      pattern: 'yyyy-ww',
      alwaysIncludePattern: true
    }
  },
  categories: {
    default: {
      appenders: ['weekly'],
      level: 'info'
    }
  }
});

const logger = log4js.getLogger();

logger.info('This message will be logged to a new file every week');