NodeJS - Creating empty array results in array with a lot of nulls

Question

I am creating a Node.js chat using socket.io
The problem is that when I see the console.log of history I see an array with A LOT of nulls and at the end my history entries [null,null,null......[ { username: 'Nobody Example', message: '231', date: '03/21/2013 14:23:58' } ]]

How come these nulls are in the array?
Here is a part of my code.

var history = [];

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

    socket.on('send', function (message) {
        var date = time();

        io.sockets.in(socket.room).emit('message', socket.username, message, date);

        history[socket.room].push({ username: socket.username, message: message, date: date });

        console.log(history);

    });

    socket.on('joinroom', function (room, username) {
        socket.room = room;
        socket.join(room);

        if ( typeof history[room] === 'undefined' )
            history[room] = [];

    });

});

Edit for more details:

The problem is in the 'joinroom' event when creating the empty array for each room.
Here are few tests that I've made:

socket.on('joinroom', function (room, username) {
    socket.room = room;
    socket.join(room);

    console.log(typeof history[room] == 'undefined');
    history[room] = [];
    console.log(typeof history[room] == 'undefined');
    console.log(JSON.stringify(history));
});

The console logs:

true
false
[null,null,null,null,..................,null,[]]

I think you want history to be an object instead of an array: var history = {}; — robertklep
– robertklep, Commented Mar 21, 2013 at 14:25
Then how am I going to add the history entry for each room? .push() is supported only by Array. — Ivan Dokov
– Ivan Dokov, Commented Mar 21, 2013 at 14:27
You're not pushing onto history directly, but on arrays in history, so that would work just fine. — robertklep
– robertklep, Commented Mar 21, 2013 at 14:29
When I change history = {} nothing really changes. The nulls are still there. I think there is something really messed up with node.js, because I test my code in the browser console (because it's just a simple work with arrays and objects) and there I get correct results (array without nulls). — Ivan Dokov
– Ivan Dokov, Commented Mar 21, 2013 at 14:48
Those nulls are a tell-tale sign of indexing an array with a large value: var a = []; a[23] = 1; console.log(JSON.stringify(a)); — robertklep
– robertklep, Commented Mar 21, 2013 at 14:50

robertklep · Accepted Answer · 2013-03-21 15:18:18Z

6

If you have an empty array and index it with a large number (like your room id's), all slots in the array before that number are filled with undefined (which translates to null in JSON).

So try making history an object instead:

var history = {};

answered Mar 21, 2013 at 15:18

robertklep

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1 Comment

Mouloud85 Over a year ago

Ooook, which translates to null in JSON, that is what led me here. Thanks.

Kishorevarma · Accepted Answer · 2013-04-30 09:56:52Z

0

try below code changing to object(hash);

var history = {};

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

socket.on('send', function (message) {
    var date = time();

    io.sockets.in(socket.room).emit('message', socket.username, message, date);

    if(history[socket.room] !== undefined) {
          history[socket.room].push = { username: socket.username, message: message, date: date   };
    } else {
        history[socket.room] = [{ username: socket.username, message: message, date: date   }];
    }

    console.log(history);

});

edited Apr 30, 2013 at 9:56

answered Mar 21, 2013 at 15:11

Kishorevarma

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1 Comment

Ivan Dokov Over a year ago

This is wrong, because it will keep only the last entry for each room. history[socket.room] = has to be array.

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