In JQuery 1.4.2 .ajax converts JSON wrong.

Question

My code worked fine in JQuery 1.3.2, but in 1.4.2 it seems to be broken. What it should get in the post is something like this:

?pks=108;pks=107

What I now get is:

?pks[]=108;pks[]=107;

When I trace this code through, the JSON object seems to be fine until it enters .ajax. Firebug, after the response is received, shows the post was:

Parameters  application/x-www-form-urlencoded
pks[]   108
pks[]   107
Source
pks%5B%5D=108&pks%5B%5D=107

Which is not what I got on JQuery 1.3.2. Where are those extra braces coming from?

Answer 1

JQuery 1.4 released a change for Nested param serialization. From their site:

jQuery 1.4 adds support for nested param serialization in jQuery.param, using the approach popularized by PHP, and supported by Ruby on Rails. For instance, {foo: ["bar", "baz"]} will be serialized as “foo[]=bar&foo[]=baz”.

In jQuery 1.3, {foo: ["bar", "baz"]} was serialized as “foo=bar&foo=baz”. However, there was no way to encode a single-element Array using this approach. If you need the old behavior, you can turn it back on by setting the traditional Ajax setting (globally via jQuery.ajaxSettings.traditional or on a case-by-case basis via the traditional flag).

The [] brackets are normally used to indicate an array, and this appears to be what they are trying to make more obvious here I think (as your query-string could be read to see that one value is being overwritten by the other).

Edit: I think you could probably follow their suggestion to use either:

// Globally set it to use the old 1.3.* way of doing things.
jQuery.ajaxSettings.traditional = true;

// Enables the 1.3.* way for a single Ajax request only
$.ajax({ data: stuff, traditional: true });