use是express調用中間件的方法，它返回一個函數。下面是一個連續調用兩個中間件的例子。 ~~~ var express = require("express"); var http = require("http"); var app = express(); app.use(function(request, response, next) { console.log("In comes a " + request.method + " to " + request.url); next(); }); app.use(function(request, response) { response.writeHead(200, { "Content-Type": "text/plain" }); response.end("Hello world!\n"); }); http.createServer(app).listen(1337); ~~~ 上面代碼先調用第一個中間件，在控制臺輸出一行信息，然后通過next方法，調用第二個中間件，輸出HTTP回應。由于第二個中間件沒有調用next方法，所以不再request對象就不再向后傳遞了。 使用use方法，可以根據請求的網址，返回不同的網頁內容。 ~~~ var express = require("express"); var http = require("http"); var app = express(); app.use(function(request, response, next) { if (request.url == "/") { response.writeHead(200, { "Content-Type": "text/plain" }); response.end("Welcome to the homepage!\n"); } else { next(); } }); app.use(function(request, response, next) { if (request.url == "/about") { response.writeHead(200, { "Content-Type": "text/plain" }); } else { next(); } }); app.use(function(request, response) { response.writeHead(404, { "Content-Type": "text/plain" }); response.end("404 error!\n"); }); http.createServer(app).listen(1337); ~~~ 上面代碼通過request.url屬性，判斷請求的網址，從而返回不同的內容。 除了在回調函數內部，判斷請求的網址，Express也允許將請求的網址寫在use方法的第一個參數。 ~~~ app.use('/', someMiddleware); ~~~ 上面代碼表示，只對根目錄的請求，調用某個中間件。 因此，上面的代碼可以寫成下面的樣子。 ~~~ var express = require("express"); var http = require("http"); var app = express(); app.use("/", function(request, response, next) { response.writeHead(200, { "Content-Type": "text/plain" }); response.end("Welcome to the homepage!\n"); }); app.use("/about", function(request, response, next) { response.writeHead(200, { "Content-Type": "text/plain" }); response.end("Welcome to the about page!\n"); }); app.use(function(request, response) { response.writeHead(404, { "Content-Type": "text/plain" }); response.end("404 error!\n"); }); http.createServer(app).listen(1337); ~~~