If you want a specific order, then you must use an array, not an object. Objects do not have a defined order.
For example, using an array, you could do this:
var myobj = [{"A":["B"]}, {"B": ["C"]}];
var firstItem = myobj[0];
Then, you can use myobj[0] to get the first object in the array.
Or, depending upon what you're trying to do:
var myobj = [{key: "A", val:["B"]}, {key: "B", val:["C"]}];
var firstKey = myobj[0].key; // "A"
var firstValue = myobj[0].val; // "["B"]