req.body.uname 不起作用是怎么回事？

错误代码： TypeError: Cannot read property 'uname' of undefined at /Users/SupermePole/Desktop/api_nodejs/app.js:21:63 at Layer.handle [as handle_request] (/Users/SupermePole/Desktop/api_nodejs/node_modules/express/lib/router/layer.js:95:5) at next (/Users/SupermePole/Desktop/api_nodejs/node_modules/express/lib/router/route.js:131:13) at next (/Users/SupermePole/Desktop/api_nodejs/node_modules/express/lib/router/route.js:125:14) at Route.dispatch (/Users/SupermePole/Desktop/api_nodejs/node_modules/express/lib/router/route.js:112:3) at Layer.handle [as handle_request] (/Users/SupermePole/Desktop/api_nodejs/node_modules/express/lib/router/layer.js:95:5) at /Users/SupermePole/Desktop/api_nodejs/node_modules/express/lib/router/index.js:277:22 at Function.process_params (/Users/SupermePole/Desktop/api_nodejs/node_modules/express/lib/router/index.js:330:12) at next (/Users/SupermePole/Desktop/api_nodejs/node_modules/express/lib/router/index.js:271:10) at expressInit (/Users/SupermePole/Desktop/api_nodejs/node_modules/express/lib/middleware/init.js:33:5)

程序代码： app.post('/', function(req, res) { res.render('index', { title: 'Hey1', message: req.body.uname } ); });

html:
    <input id="uname" name="uname" type="text" value="" />