javascript - Canvas 未在 router.get 方法中更新

Question

这是我第一次在 Node.js 应用程序中使用路由器。通常，我只会编写一个 HTML 页面，但这里我使用 Jade 模板。我的问题是，页面按照用 Jade 编写的方式呈现，而没有对我在您在此处看到的 index.js 脚本中编写的 Canvas 进行任何更改。是否有特定的函数可以通过这些更改重新呈现页面？

index.js:

var express = require('express');
var router = express.Router();

/* GET home page. */
router.get('/', function(req, res, next) {
  res.render('index', { title: 'Express' });
  var canvas = document.getElementById("myCanvas");
  canvas.width = document.body.clientWidth;
  canvas.height = document.body.clientHeight;
  var context = canvas.getContext("2d");
  context.fillStyle = "#FF0000";
  context.fillRect(0,0,150,75);
});

module.exports = router;

索引.jade:

extends layout

block content
  h1= title
  p Welcome to #{title}
  canvas#myCanvas(width='200', height='100', style='border:1px solid #000000;')

app.js:

var express = require('express');
var path = require('path');
var favicon = require('serve-favicon');
var logger = require('morgan');
var cookieParser = require('cookie-parser');
var bodyParser = require('body-parser');

var routes = require('./routes/index');
var users = require('./routes/users');

var app = express();

// view engine setup
app.set('views', path.join(__dirname, 'views'));
app.set('view engine', 'jade');

// uncomment after placing your favicon in /public
//app.use(favicon(path.join(__dirname, 'public', 'favicon.ico')));
app.use(logger('dev'));
app.use(bodyParser.json());
app.use(bodyParser.urlencoded({ extended: false }));
app.use(cookieParser());
app.use(express.static(path.join(__dirname, 'public')));

app.use('/', routes);
app.use('/users', users);

// catch 404 and forward to error handler
app.use(function(req, res, next) {
  var err = new Error('Not Found');
  err.status = 404;
  next(err);
});

// error handlers

// development error handler
// will print stacktrace
if (app.get('env') === 'development') {
  app.use(function(err, req, res, next) {
    res.status(err.status || 500);
    res.render('error', {
      message: err.message,
      error: err
    });
  });
}

// production error handler
// no stacktraces leaked to user
app.use(function(err, req, res, next) {
  res.status(err.status || 500);
  res.render('error', {
    message: err.message,
    error: {}
  });
});


module.exports = app;

Answer 1

您无法访问服务器端的document对象。正如我所看到的，您已经在 app.js 文件中调用了 bodyParser 中间件，所以现在您需要做的就是在 jade 文件中为 Canvas 命名 canvas(name="myCanvas")

并在index.js中从req.body访问 Canvas :

router.get('/', function(req, res, next) {
    //req.body object contains your element
    var canvas = req.body.myCanvas;
    //...
    res.render('index', { title: 'Express' });
});