javascript object within object issue

Question

I am trying to get the first object within an object.

I have something like

var object = {
     task:{
       config:'auto',
       title :'test'
     },
     prop:'switch',
     time:'5min'
}

My problem is task object could be named differently. so it could be

var object = {
     task2:{
       config:'manual',
       title :'test2'
     },
     prop:'switch',
     time:'5min'
}

I can't use object.task1.config because task name could changed. The task object will always be the first object though.

I want to get the task object no matter what name it has. How do I accomplish that? Thanks!

Could it have other properties than prop, time or the one you want ? — Ibrahim Najjar
– Ibrahim Najjar, Commented Nov 13, 2013 at 20:42
no it won't have other properties. I just need to get the first task object. — FlyingCat
– FlyingCat, Commented Nov 13, 2013 at 20:43
@FlyingCat are there other properties in the object that are also objects, or is task the only one? — jbabey
– jbabey, Commented Nov 13, 2013 at 20:47
Objects properties don't really have a concept of "first" - if you need properties to be in a specific order you have to use an array. — nnnnnn
– nnnnnn, Commented Nov 13, 2013 at 20:48

jbabey · Accepted Answer · 2013-11-13 20:56:43Z

2

To get the first property value of an object in modern browsers you could use the Object.keys method:

var myObject = {
    whoTheHellKnows: 'foo',
    notUsed: 'whatever'
};

var firstProperty = myObject[Object.keys(myObject)[0]];

Working example

Edit: if you do not trust the ordering of the properties (which you should not) AND the task object is the only nested object in your objects, you can rely on type interrogation to find it:

var myObject = {
    task123215452: { dahKey: 'foo' },
    notUsed: 'whatever',
    somethingElse: 42
};

var taskObject;

for (var key in myObject) { 
    if (typeof myObject[key] === 'object' && !(myObject[key] instanceof Array)) {
        taskObject = myObject[key];
        break;
    }
}

Working example

edited Nov 13, 2013 at 20:56

answered Nov 13, 2013 at 20:43

jbabey

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5 Comments

Ibrahim Najjar Over a year ago

Is Object.Keys() guaranteed to return the keys in the same order they were defined ?

bfavaretto Over a year ago

No, there's no guarantee regarding the order.

jbabey Over a year ago

From the docs: "The ordering of the properties is the same as that given by looping over the properties of the object manually."

bfavaretto Over a year ago

@jbabey ...which is implementation-dependent

jbabey Over a year ago

@bfavaretto my edit should be order-independent, though it relies on there only being a single nested object literal.

bfavaretto · Accepted Answer · 2013-11-13 20:48:32Z

2

If you need to access the first key and you don't know the key name, you should really be using an array instead of an object. Objects don't have the concept of a "first" key.

If that's not an option, you're left with for..in or Object.keys, which may fail on some JavaScript implementations because the language specification does not enforce the order of object key enumerations. However, in practice, it will work on current browsers, as they all iterate the keys in the order they were declared^{citation needed thanks to jbabey}.

answered Nov 13, 2013 at 20:48

bfavaretto

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2 Comments

jbabey Over a year ago

Your citation: "all major browsers support an iteration order based on the earliest added property coming first"

bfavaretto Over a year ago

Interesting IE edge case mentioned there!

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