jquery 之 selector 一

对于jquery的selector核心就是jquery.find方法，从github上可以看到有native和sizzle两种实现

首先分析下native实现，源码（jquery 2.1.0）selector-native之jQuery.find函数实现如下

find: function( selector, context, results, seed ) {
		var elem, nodeType,
			i = 0;

		results = results || [];
		context = context || document;

		// Same basic safeguard as Sizzle
		if ( !selector || typeof selector !== "string" ) {
			return results;
		}

		// Early return if context is not an element or document
		if ( (nodeType = context.nodeType) !== 1 && nodeType !== 9 ) {
			return [];
		}

		if ( seed ) {
			while ( (elem = seed[i++]) ) {
				if ( jQuery.find.matchesSelector(elem, selector) ) {
					results.push( elem );
				}
			}
		} else {
			jQuery.merge( results, context.querySelectorAll(selector) );
		}

		return results;
	}

其实核心就一句

context.querySelectorAll(selector)

换句话说selector的实现是基于querySelectorAll的。

注意到selector-native中一段注释

/*
	* Optional (non-Sizzle) selector module for custom builds.
	*
	* Note that this DOES NOT SUPPORT many documented jQuery
	* features in exchange for its smaller size:
	*
	* Attribute not equal selector
	* Positional selectors (:first; :eq(n); :odd; etc.)
	* Type selectors (:input; :checkbox; :button; etc.)
	* State-based selectors (:animated; :visible; :hidden; etc.)
	* :has(selector)
	* :not(complex selector)
	* custom selectors via Sizzle extensions
	* Leading combinators (e.g., $collection.find("> *"))
	* Reliable functionality on XML fragments
	* Requiring all parts of a selector to match elements under context
	* (e.g., $div.find("div > *") now matches children of $div)
	* Matching against non-elements
	* Reliable sorting of disconnected nodes
	* querySelectorAll bug fixes (e.g., unreliable :focus on WebKit)
	*
	* If any of these are unacceptable tradeoffs, either use Sizzle or
	* customize this stub for the project's specific needs.
	*/

大致意思是说native的实现方式会导致部分jquery的功能不支持虽然说代码更少。

再回到querySelectorAll，它是一个支持css selector 的函数，详见nodeselector