Node.js / Express / JavaScript scope issue

Question

I'm working on the following Node.js webapp, with handlebars and express for templating and routing. But a problem arises in the app.get('/', function(){ ... }) block.

The problem is that when it runs, it says it Cannot read property 'getData' of undefined at Object.<anonymous> (C:\\Users\\natha\\Documents\\GitHub\\HAS\\webUI\\app.js:19:23)

var port     = 3000,
fs       = require('fs'),
exec     = require('child_process'),
express  = require("express"),
exphbs   = require("express3-handlebars"),
app      = express(),
Database = require('./db/Database.js'),
db       = new Database().selectDB('lights')
hbs      = exphbs.create({ defaultLayout: 'main'});


app.engine('handlebars', hbs.engine);
app.set('view engine','handlebars');
var io = require('socket.io').listen(app.listen(port))
app.enable('view cache');
app.use(express.static(__dirname + '/public'));

app.get('/',function(request, response){
    var data = this.db.getData();
    response.render('home', {
        helpers: {
           client: data.clients
        }
    });
});

io.sockets.on('connection', function (socket) {
    updateClients();



    socket.on('news', function(data, error){
        console.log(this.db);
    }.bind(this));
    socket.on('disconnect', function(){
        updateClients();
        console.log('hi');
    });

}.bind(this));

var updateClients = function(){
    var clients = [];
    io.sockets.clients().forEach(function(data){
        clients.push(data.id);
    });

    io.sockets.emit('news', { 
        users: clients
    });
}

I'm 100% sure it's not a asynchronous function problem, because when the socket.on('news', ....) runs which is triggered by a client far after the DB has initialized, it successfully prints the database info including the data..

This has to be a scope issue but I can't seem to fix it.

Answer 1

只需删除this ，db只是一个变量，所以它应该是db.getData()