Does jQuery Really Support All CSS3 Selectors, Including :nth-last-child()?

jQuery's Support for CSS3 Selectors: An In-Depth Examination

While jQuery claims to support a wide range of CSS selectors, the question of whether it truly supports selectors like :nth-last-child() has resurfaced. Let's delve into this topic and understand the limitations and exceptions.

Limited Support for CSS3 Selectors

Despite stating compliance with Selectors Level 3, jQuery does not fully implement the standard. Its selector documentation clarifies that it incorporates elements from CSS 1-3 and adds its own custom selectors.

Exception: :nth-last-child() and Other Level 3 Selectors

Starting with jQuery 1.9, nearly all Level 3 selectors are supported in the Sizzle selector library, except for a handful of limitations:

• Dynamic pseudo-classes: jQuery cannot resolve classes like :link and :focus since they require event handlers rather than pseudo-classes.
• Namespace prefixes: Namespacing in CSS is not supported by jQuery.
• Missing Selectors: The following Level 3 selectors are not implemented in jQuery 1.8 or older: :target, :root, :nth-last-child(), and others. Additionally, :lang() is also missing.

Fallbacks and Compatibility

jQuery uses the native document.querySelectorAll() implementation whenever possible. If document.querySelectorAll() fails or is not supported, jQuery falls back to Sizzle. This means that selectors like :nth-last-child() may work in browsers that support them natively, even if jQuery itself does not.

Recommendation:

If you require full support for Level 3 selectors like :nth-last-child(), it is recommended to upgrade to jQuery 1.9 or later, which adds support for these selectors while maintaining compatibility with older IE versions. Alternatively, consider using jQuery's custom selector extensions to implement the missing selectors yourself.

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