Javascript: Weird error when working with JS Objects

Question

So I've been encountering this error quite a bit lately and it looks like this...

Main.js:84 Uncaught TypeError: Cannot set property 'CurrParent' of undefined

And basically I have a couple draggable elements all of which have an attribute called "c_index" which is set to an integer, and what i'm doing with them is using them in another file which is going to act as some sort of a metadata file, and that's where the problem is: I'm storing the "c_index" of the element currently being dragged in a var called CI it looks like this:

var CI = event.relatedTarget.getAttribute("c_index");

and i'm using it like this:

Meta.elements.CI.CurrParent = 'workspace';

and the object that i'm trying to save into looks like this without editing:

var Meta = { 
    elements : { 
    } 
}

Any help would be much appreciated :)
p.s: I'm using a framework called interact.js

That's not "weird". It just means that Math.elements.CI is undefined. — Pointy
– Pointy, Commented Jan 26, 2017 at 14:18
Your var CI = ... code won't magically produce a CI property on Meta.elements. You'd want Meta.elements.CI = event.relatedTarget.getAttribute("c_index");. But note that that property will have a primitive string as a value. Setting a property on that primitive string later (Meta.elements.CI.CurrParent = ...) is a long-winded no-op (it won't be kept). It would temporarily create a string object, set the property on the string object, and then throw the string object away, with no effect at all on Meta.elements.CI. — T.J. Crowder
– T.J. Crowder, Commented Jan 26, 2017 at 14:19
@T.J.Crowder you almost got it but i want it to create a new child object that is called whatever value CI outputs that I can then write into. — Zyad-O
– Zyad-O, Commented Jan 26, 2017 at 14:29
@T.J.Crowder No problem, I understand my wording is all over the place, what i wanted to say is, I have a file, which by default has two nested objects the outer one being called Meta and the inner one being called elements, what i want to do is dynamically create another object called l1 (which corresponds to the c-index in this case) inside of elements. — Zyad-O
– Zyad-O, Commented Jan 26, 2017 at 14:39

T.J. Crowder · Accepted Answer · 2017-01-26 14:43:13Z

0

From a comment on the question:

...what i want to do is dynamically create another object called l1 (which corresponds to the c-index in this case) inside of elements

If I'm understanding you correctly, you'd want to use the value of c_index as the property name, via brackets notation. If you want that object to have a CurrParent property with the value "workspace", you can initialize that at the same time:

var ci = event.relatedTarget.getAttribute("c_index");
Meta.elements[ci] = {CurrParent: "workspace"};

answered Jan 26, 2017 at 14:43

T.J. Crowder

1.1m201 gold badges2k silver badges2k bronze badges

Thanks for the answer, you really helped me out in the long run!

Zyad-O
– Zyad-O

01/26/2017 14:48:07
Commented Jan 26, 2017 at 14:48

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