merge json object with arrays - json

Question

Suppose I have two json objects and I need to merge them.
css: [{
drag: "mode() == 'layout'",
ui_draggable: "mode() == 'layout'"
}]
css: [{
someclass : true
}]
I want to end up with:
css: [{
drag: "mode() == 'layout'",
ui_draggable: "mode() == 'layout'",
someclass : true
}]
After some further trial I came up with this but I assume I have place a few bugs or useless lines of code in it.
I came up with this code after a little playing around. My needs didn't need to recurse more than two levels so this is just fine. It could be much refined I am sure but it works great for binding knockout. Here is an example of how I used it to extend jquery unobtrusive knockoutjs
var settings = {
text: 'SelectedCard().CardData.Title',
visible: "mode() != 'edit' || !isMyCard()",
css: [{ drag: "mode() == 'layout'" , selectedElement: "selectedCardElement() == '_titlePreview'"}]
};
var settings2 =
{
css: [{ drag: "mode() == 'layout'"}]
};
var settings3 = merge(settings, settings2);
function merge(first, second) {
for (var a1 in first) {
// if second object is null we are finished.
used.push(a1);
if (second[a1] == null) {
continue;
} else {
var ob2 = second[a1];
if (typeof (first[a1]) != typeof (ob2)) {
throw new Error("conflicting properties named:" + a1);
}
if ($.isArray(first[a1])) {
for (var i = 0; i < ob2.length; i++) {
first[a1].push(ob2[i]);
}
} else {
// matching property.
return merge(first[a1], second[a1]);
}
}
}
for (var a2 in second) {
if (used.indexOf(a2) < 0) {
first[a2] = second[a2];
}
}
return first;
}

Answer 1

1) To merge both objects with a one-way overwrite, this will do it:
for (var attrname in obj2) {
obj1[attrname] = obj2[attrname];
}
2) To merge selectively, both ways:
obj1.someclass = obj2.someclass;
-or-
obj2["someclass"] = obj1["someclass"];
In this case, if the property does not yet exist in the object it does not need to be defined before assigning it.
3) Consider using a library like Underscore.js for performing "array functions" similar to this:
_.union([1, 2, 3], [101, 2, 1, 10], [2, 1]);
returns [1, 2, 3, 101, 10]
4) Lastly, here's a strong resource for formatting JSON objects, arrays and a combination thereof: jsonexample.com. This will be helpful as you get into complex "array functions".
Cheers!