Undefined value after conversion from JSON array to object

Question

I have JSON array with one object consisting of nodes and links.

data = [Object]=[ { nodes: Array[..] ,links: Array[…] } ]

This is all fine, but for accessing the links for example I have to use data[0].links, which is a bit annoying. I would like the array to be an object, so that data.links gives access to the links. I have tried to set:

data = data[0];

But then the array of Objects, data.links, are displayed as "undefined".It seems like when a specific element is accessed the value is displayed, for example data.links[3].name. Why is that?

Edit:

More specifically:

if data = [ { nodes: Array[... ] ,links: Array[...] } ] =>

console.log(data[0].links); //shows the data[0].links[0].name = value in the console

if data = { nodes: Array[... ] ,links: Array[...] } =>

console.log(data.links); //shows data[0].links[0].name = undefined

but interestingly

console.log(data.links[0].name); //shows the correct value.

What is this notation? In JS, [Object] is an array containing the builtin object constructor, and Array[foo] looks up the property on the Array constructor whose name is the result of evaluating foo. — Mike Samuel
– Mike Samuel, Commented Nov 2, 2012 at 21:14
'then the array of Objects, data.links, are displayed as "undefined"' - Displayed how? Please show more of your code, and perhaps a more real-world example of your data that is actually valid JS. For the data you show, after doing data=data[0] if you say data.links it will give you the links array, so then you'd have to access the individual links with data.links[0], etc. (By the way, there is no JSON anywhere in your question - JSON is a string format.) — nnnnnn
– nnnnnn, Commented Nov 2, 2012 at 21:15

Mike Brant · Accepted Answer · 2012-11-02 21:15:47Z

1

A couple of solutions:

If you control the JSON output, simply remove the enclosing brackets [] those are basically wrapping your object in an array.

data = { nodes: [...] ,links: [...] };

If you don't control the JSON just simply assign the zero index of the array to the variable you actually want to work with.

json = [ { nodes: [...] ,links: [...] } ];
data = json[0];

Unfortunately, 'links' is an array. To access a member of that array, you will need to access its index value.

answered Nov 2, 2012 at 21:15

Mike Brant

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2 Comments

graphmeter Over a year ago

Thanks for the answer, directly setting it without the brackets works fine. However, I still have the same issue with the undefined values in the nodes and links arrays when looking at the object in developer tools. For example: data.nodes[1].name = "undefined".

nnnnnn Over a year ago

@graphmeter - That's because nodes is an array and doesn't have a name property - the items in the array have a name property (presumably; you don't show it in the question). You have to say data.nodes[0].name for the first one; use a variable in a loop to access each in turn.

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