lib/index.js
function(required, cb) {
      var chain = new Chain(config);
      chain.on(required, cb);
      return chain;
    }
function(required, cb) {
      var chain = new Chain(config);
      chain.on(required, cb);
      return chain;
    }
function ( required , cb ) { var chain = new Chain ( config ) ; chain . on ( required , cb ) ; return chain ; }
EventChain factory.

@param required
The list of events that are required before invoking the callback function.
@param cb
The callback to invoke after all required events have been fired.

@returns {Chain|exports|module.exports}
EventChain factory .