Determine fluid or fixed width in JavaScript

Is there a reliable way to tell whether a web page's layout is fixed or fluid? I don't care if it required a library like jQuery or MooTools so long as it's rea开发者_如何学编程sonably accurate.

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Typical width methods are going to give you pixels, but there's an answer here which should give you (in most cases) a percentage width if it is defined as such: get CSS rule's percentage value in jQuery

Suspected caveats with this method:

• The width is declared in the first stylesheet (this could be modified as appropriate to search all stylesheets).
• The width isn't an inline style.
• You know the major container element of the page (this would be an issue with any method).