code: function loadParser (parserName) {
    var parser = parsers[parserName]
  
    if (parser !== undefined) {
      return parser
    }
  
    // this uses a switch for static require analysis
    switch (parserName) {
      case 'json':
        parser = require('./lib/types/json')
        break
      case 'raw':
        parser = require('./lib/types/raw')
        break
      case 'text':
        parser = require('./lib/types/text')
        break
      case 'urlencoded':
        parser = require('./lib/types/urlencoded')
        break
    }
  
    // store to prevent invoking require()
    return (parsers[parserName] = parser)
  }
docs: Load a parser module.
  @private