lib/modules/sortCursor.js
function getMongoSortArray (field, prefix) {
  return (!field.startsWith('-'))
    ? [prefix + field, 1]
    : [prefix + field.substr(1), -1];
}
function getMongoSortArray (field, prefix) {
  return (!field.startsWith('-'))
    ? [prefix + field, 1]
    : [prefix + field.substr(1), -1];
}
function getMongoSortArray ( field , prefix ) { return ( ! field . startsWith ( '-' ) ) ? [ prefix + field , 1 ] : [ prefix + field . substr ( 1 ) , - 1 ] ; }
flips sorting order if field begins with minus '-'
@param {String} field
@param {String} prefix
@returns {Array<Array>}
flips sorting order if field begins with minus -