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jQuery:掌握選擇器

選擇器至少可以追溯到“CSS選擇器”。jQuery的源代碼中內(nèi)嵌了一個(gè)叫Sizzle的對象，其實(shí)就是選擇器了。在jQuery官網(wǎng)上顯示Sizzle屬于“Other jQuery Foundation Projects”，Sizzle能夠獨(dú)立為一個(gè)單獨(dú)的項(xiàng)目，由此不難體會(huì)到選擇器的重要性。看看下面三個(gè)頁面，相比之下，jQuery選擇器官方文檔看起來是最“亂”的。

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  1. http://www.w3.org/TR/css3-selectors
  2. CSS選擇器W3C標(biāo)準(zhǔn)文檔
  3.  
  4. https://github.com/jquery/sizzle/wiki/Sizzle-Documentation
  5. Sizzle文檔
  6.  
  7. http://api.jquery.com/category/selectors/
  8. jQuery選擇器官方文檔

jquery1.9.0源代碼有這樣一行：

  1. jQuery.find = Sizzle; 
 
導(dǎo)入jquery.js和sizzle.js，可以看到j(luò)Query.find和Sizzle確實(shí)是一回事。
 
  1. iJs.showObjectNames("window.jQuery.find");  
  2. iJs.showObjectNames("window.Sizzle"); 

    [Object] window.jQuery.find
        |--[function] attr
        |--[function] compile
        |--[function] contains
        |--[function] error
        |--[function] getText
        |--[function] isXML
        |--[function] matches
        |--[function] matchesSelector
        |--[function] setDocument
        |--[function] uniqueSort
        |--[object] selectors
    
    [Object] window.Sizzle
        |--[function] attr
        |--[function] compile
        |--[function] contains
        |--[function] error
        |--[function] getText
        |--[function] isXML
        |--[function] matches
        |--[function] matchesSelector
        |--[function] setDocument
        |--[function] uniqueSort
        |--[object] selectors
 
既然Sizzle自稱"supports virtually all CSS 3 Selectors"，那么不妨就參考下面W3C描述吧，再難找到更好的文檔片斷了（點(diǎn)擊鏈接可查看語法細(xì)節(jié)），不是么？
 (備注：這個(gè)Table貼過來總是出現(xiàn)顯示問題，于是對html代碼進(jìn)行了編輯，其中一個(gè)替換是(]*">)[^<]*()替換為$1更多$2)
語法 含義 鏈接 版本
* any element 更多 2
E an element of type E 更多 1
E[foo] an E element with a "foo" attribute 更多 2
E[foo="bar"] an E element whose "foo" attribute value is exactly equal to "bar" 更多 2
E[foo~="bar"] an E element whose "foo" attribute value is a list of whitespace-separated values, one of which is exactly equal to "bar" 更多 2
E[foo^="bar"] an E element whose "foo" attribute value begins exactly with the string "bar" 更多 3
E[foo$="bar"] an E element whose "foo" attribute value ends exactly with the string "bar" 更多 3
E[foo*="bar"] an E element whose "foo" attribute value contains the substring "bar" 更多 3
E[foo|="en"] an E element whose "foo" attribute has a hyphen-separated list of values beginning (from the left) with "en" 更多 2
E:root an E element, root of the document 更多 3
E:nth-child(n) an E element, the n-th child of its parent 更多 3
E:nth-last-child(n) an E element, the n-th child of its parent, counting from the last one 更多 3
E:nth-of-type(n) an E element, the n-th sibling of its type 更多 3
E:nth-last-of-type(n) an E element, the n-th sibling of its type, counting from the last one 更多 3
E:first-child an E element, first child of its parent 更多 2
E:last-child an E element, last child of its parent 更多 3
E:first-of-type an E element, first sibling of its type 更多 3
E:last-of-type an E element, last sibling of its type 更多 3
E:only-child an E element, only child of its parent 更多 3
E:only-of-type an E element, only sibling of its type 更多 3
E:empty an E element that has no children (including text nodes) 更多 3
E:link
E:visited		 an E element being the source anchor of a hyperlink of which the target is not yet visited (:link) or already visited (:visited) 更多 1
E:active
E:hover
E:focus		 an E element during certain user actions 更多 1 and 2
E:target an E element being the target of the referring URI 更多 3
E:lang(fr) an element of type E in language "fr" (the document language specifies how language is determined) 更多 2
E:enabled
E:disabled		 a user interface element E which is enabled or disabled 更多 3
E:checked a user interface element E which is checked (for instance a radio-button or checkbox) 更多 3
E::first-line the first formatted line of an E element 更多 1
E::first-letter the first formatted letter of an E element 更多 1
E::before generated content before an E element 更多 2
E::after generated content after an E element 更多 2
E.warning an E element whose class is "warning" (the document language specifies how class is determined). 更多 1
E#myid an E element with ID equal to "myid". 更多 1
E:not(s) an E element that does not match simple selector s 更多 3
E F an F element descendant of an E element 更多 1
E > F an F element child of an E element 更多 2
E + F an F element immediately preceded by an E element 更多 2
E ~ F an F element preceded by an E element 更多 3
 
需注意，jQuery()和jQuery.find()返回的對象類型是不一樣的，前者是jQuery.fn，后者是Sizzle。例如，jQuery('html body div#dbg');和jQuery.find('html body div#dbg');都是“選擇”了id為dbg的div，但是前者表示為jQuery.fn對象，后者表示為Sizzle對象。

選擇器的語法是有標(biāo)準(zhǔn)的，逐一嘗試每一種寫法沒有必要，今天學(xué)會(huì)了也許明天就忘記，不如有文檔在手，用到時(shí)再翻閱。需要想一想的是選擇器的價(jià)值所在，從根本上來講，選擇器就是幫助我們避免了遍歷DOM（或者也包括XML?）的麻煩。一個(gè)兩個(gè)的遍歷代碼其實(shí)也不難寫，但是網(wǎng)頁上的互動(dòng)多了就麻煩了，下面是一個(gè)隔行選取的代碼片斷，不難體會(huì)其中運(yùn)用選擇器的奧妙所在：

  1.  
  2.     ...測試1... 
  3.     ...測試2... 
  4.     ...測試3... 
  5.     ...測試4... 
 
  •  
  •    
  •     var $myObj = jQuery('div b:nth-child(even)');//選擇器  
  •     $myObj.each(  
  •         function(i){  
  •             var tTemp = jQuery(this).text();  
  •             iJs.put(tTemp);//輸出選擇結(jié)果  
  •         });  
  •  
    • 調(diào)試信息:
        ...測試2...
        ...測試4...

    網(wǎng)站名稱：jQuery:掌握選擇器
    本文來源：http://weahome.cn/article/piceio.html

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