code: function Router(opts) {
    if (!(this instanceof Router)) {
      return new Router(opts);
    }
  
    this.opts = opts || {};
    this.methods = this.opts.methods || [
      'HEAD',
      'OPTIONS',
      'GET',
      'PUT',
      'PATCH',
      'POST',
      'DELETE'
    ];
  
    this.params = {};
    this.stack = [];
    this.MATCHS = {};
  }
docs: Create a new router.
  
  @example
  
  Basic usage:
  
  ```javascript
  var app = require('koa')();
  var router = require('koa-router')();
  
  router.get('/', function *(next) {...});
  
  app
  .use(router.routes())
  .use(router.allowedMethods());
  ```
  
  @alias module:koa-router
  @param {Object=} opts
  @param {String=} opts.prefix prefix router paths
  @constructor