how to refer to json fields

Question

Let's asume that I have json variable:

var json ={"A":"a","B":"b","x":"y","a":"b"}

When I want to refer to A i just write json.A

How to do it when I have key in a variable, ie:

var key = "A";

Is there any function that returns value or null (if key isn't in json)?

Answer 1

Use bracket notation, like this:

var key = "A";
var value = json[key];

In JavaScript these two are equivalent:

object.Property
object["Property"];

And just to be clear, this isn't JSON specific, JSON is just a specific subset of object notation...this works on any JavaScript object. The result will be undefined if it's not in the object, you can try all of this here.

Answer 2

How about:

json[key]

Try:

json.hasOwnProperty(key)

for the second part of your question (see http://stackoverflow.com/questions/1098040/checking-if-an-associative-array-key-exists-in-javascript)