Javascript best practices - Using server-side values

Question

For the past few years I have always used a client-side hidden <input> field to store a server-side value and use it in Javascript land.

For example, let's say I need an Ajax timeout value from my app configuration.

I'd probably store it like this in my JSP:

<input type="hidden" id="ajaxTimeout" value="${serverValue}" />

and then use it like this where my AJAX call lived in an external file:

$("#ajaxTimeout").val()

I was having a discussion about this today and it was suggested that it is best practice to store values which are only going to be used by Javascript within HTML <meta> tags.
Does this matter? Is there a preferred way to obtain server-side information which is solely to be used in Javascript?
My understanding is that if the hidden input field is not part of a form then it is safe enough to use to store value as it won't be attached to any requests. Having said that, I've always thought this was indeed a bit of a hack.

Thoughts?

::EDIT::
Two fantastic answers:

• Use objects literals for general in-page data that is not tied to any particular DOM element.
• Use data attributes to store custom data tied to DOM elements: http://www.w3.org/TR/2010/WD-html5-20101019/elements.html#attr-data

Answer 1

In addition to the plain old object literal method given in other answers, if the value you want to pass to the client is about a specific DOM element (or there is a DOM element that represents the logical object that the value is about), you can put the value in a data attribute:

<div id="videoplayer" data-startplayingat="1:02">HTML Content</div>

This is accessible as an entire attribute, data-startplayingat, or in modern browsers there is the dataset attribute. jQuery syntax is $('#videoplayer').data('startplayingat').

The official W3C spec on data attributes explains all this.

Here are a few interesting highlights:

• The name must not use upper case letters, and must be XML compatible.
• The dataset attribute converts dashes, such that a name like start-playing will become startPlaying.

One potential drawback for the object literal method (which I like and have used myself) is that if you want the object in a .js file, then normally static javascript files have to be run through your dynamic parser--which will cause a potentially small (but still present) performance loss. Putting the object declaration into a <script> tag in an HTML file works around this, but then you can have script load order issues to deal with.