text: import { FORMAT_DEFAULT } from '../../constant'
  
  export default (o, c) => { // locale needed later
    const proto = c.prototype
    const oldFormat = proto.format
    // extend en locale here
    proto.format = function (formatStr) {
      const yearBias = 543
      const { padStart } = this.$utils()
      const str = formatStr || FORMAT_DEFAULT
      const result = str.replace(/BBBB|BB/g, (match) => {
        const year = String(this.$y + yearBias)
        const args = match === 'BB' ? [year.slice(-2), 2] : [year, 4]
        return padStart(...args, '0')
      })
      return oldFormat.bind(this)(result)
    }
  }
  