表达回应
Express Responses将方法附加到res以使返回的HTTP错误更轻松，更一致。
npm install express-responses
var app = require ( 'express' ) ( ) ;
var responses = require ( 'express-responses' ) ;
app . use ( responses ( {
view : 'http-error' ,
emit : function ( error ) { ... }
} ) ) ;
app . get ( '/users/:user' , function ( req , res , next ) {
var user = db . getUser ( req . params . user ) ;
if ( ! user ) {
// retu
