javascript object of object editing

Question

I have the following code, which doesn't work.

var conversations = { };
conversations['5634576'].name = 'frank';

Apparently I cannot create objects inside objects. I wanted to use the conversation object to store arrays of objects to keep a history of messages client-side with localStorage to save space server side.

But apparently, I cannot even create variables inside the object, unless they already exist, like this:

var conversations = { 123: { name: 'test' } };
conversations[123].name = "frank";

But, since I will not know the IDs that will be used, I have no idea how workaround this problem.

Any ideas?

var conversations = {}; conversations['5634576'] = {}; conversations['5634576'].name = 'frank';, you can check if the second step is necessary using if (!conversations.hasOwnProperty('5634576')) { /*..*/ } — Paul S.
– Paul S., Commented Feb 23, 2013 at 17:51
Or var conversations = { }; conversations['5634576'] = {name: 'frank'}. "what a hassle.": well, what do you expect? You are trying to access the value at property '5634576', which does not exist. Please read MDN - Working with Objects. — Felix Kling
– Felix Kling, Commented Feb 23, 2013 at 17:52
but, when the user receives a new message, the object is re-created, therefore rewriting it, with the string example you cannot see it but, imagine it being an array: it will be a problem. — john smith
– john smith, Commented Feb 23, 2013 at 17:56
@john: Only initialize the object/array/whatever if it does not exist yet. — Felix Kling
– Felix Kling, Commented Feb 23, 2013 at 17:58

ATOzTOA · Accepted Answer · 2013-02-23 17:58:22Z

3

You need to do like this:

// Create an object
var conversations = {};

// Add a blank object to the object if doesn't already exist
if (!conversations.hasOwnProperty('5634576')) {
    conversations['5634576'] = {};
}

// Add data to the child object
conversations['5634576'].name = 'frank';

The object will look like this:

conversations{
    '5634576': {
        name : 'frank'
    }
}

Update

You can check if the element exist using in

if('5634576' in conversations) {
    // Exist
}

edited Feb 23, 2013 at 17:58

answered Feb 23, 2013 at 17:52

ATOzTOA

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4 Comments

john smith Over a year ago

what about arrays? if i instantiate the array like this -> conversations['5634576'].messages = []; conversations['5634576'].messages.push(message); i will lose the previous messages. can I prevent this?

Fabrício Matté Over a year ago

conversations['5634576'] = conversations['5634576'] || {}; conversations['5634576'].messages = conversations['5634576'].messages || [];

Felix Kling Over a year ago

@john: Only do conversations['5634576'].messages = []; when .messages does not exit yet. Obviously you will loose any previous value when you assign a new value.

ATOzTOA Over a year ago

@johnsmith If you do push, you won't lose previous messages.

sdespont · Accepted Answer · 2013-02-23 17:54:26Z

0

In your code, you can't add a variable to the index '5634576' because it is not still existing.

var conversations = { };
conversations['5634576'].name = 'frank';

You need to create it, then assign the valriable

var conversations = { };
conversations['5634576'] = {};
conversations.name = 'frank';

answered Feb 23, 2013 at 17:54

sdespont

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Comments

dfsq · Accepted Answer · 2013-02-23 17:54:38Z

0

Maybe the shortest possible way:

var conversations = {};
(conversations['5634576'] = {}).name = 'frank';

answered Feb 23, 2013 at 17:54

dfsq

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Comments

LetterEh · Accepted Answer · 2013-02-23 18:03:29Z

0

// build this how you were
conversations = {};

// if conversations[12345] is defined, use it:
// else set it to an object with the desired properties/methods
conversations["12345"] = conversations["12345"] || { name : "Frank", messages : [] };
conversations["12345"].messages.push(new_msg);

I'm assuming you're going to be doing this within a function, XHR or otherwise

conversations.add_message = function (msg) {
    var id = msg.conversation_id;
    conversations[id] = conversations[id] ||
                        conversations.new_conversation(msg.user_name); // returning a conversation object
    conversations[id].messages.push(msg);
};


conversations.new_conversation = function (name) {
    return { name : name, messages : [], etc : {} };
};

edited Feb 23, 2013 at 18:03

answered Feb 23, 2013 at 17:58

LetterEh

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