code: function formatArray (array, options) {
    if (Array.isArray(array)) {
      let str = '['
      const len = array.length
      for (let i = 0; i < len; i++) {
        if (i !== 0) {
          str += ', '
        }
        str += formatArray(array[i], options)
      }
      str += ']'
      return str
    } else {
      return format(array, options)
    }
  }
docs: Recursively format an n-dimensional matrix
  Example output: "[[1, 2], [3, 4]]"
  @param {Array} array
  @param {Object | number | Function} [options]  Formatting options. See
  lib/utils/number:format for a
  description of the available
  options.
  @returns {string} str