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3.1 源码
init: function( selector, context, rootjQuery ) {var match, elem, ret, doc;// Handle $(""), $(null), or $(undefined)//如果selector为空格,!selector为falseif (!selector) {//此时this为空jQuery对象return this;}// Handle $(DOMElement)//nodeType节点类型,利用是否有nodeType属性来判断是否是DOM元素if ( selector.nodeType ) {//将第一个元素和属性context指向selectorthis.context = this[0] = selector;this.length = 1;return this;}// The body element only exists once, optimize finding it//因为body只出现一次,利用!context进行优化if ( selector === "body" && !context && document.body ) {//context指向document对象this.context = document;this[0] = document.body;this.selector = selector;this.length = 1;return this;}// Handle HTML stringsif ( typeof selector === "string" ) {// Are we dealing with HTML string or an ID?//以<开头以>结尾,且长度大于等于3,这里假设是HTML片段,跳过queckExpr正则检查if ( selector.charAt(0) === "<" && selector.charAt( selector.length - 1 ) === ">" && selector.length >= 3 ) {// Assume that strings that start and end with <> are HTML and skip the regex checkmatch = [ null, selector, null ];} else {match = quickExpr.exec( selector );}// Verify a match, and that no context was specified for #idif ( match && (match[1] || !context) ) {// HANDLE: $(html) -> $(array)if ( match[1] ) {context = context instanceof jQuery ? context[0] : context;doc = ( context ? context.ownerDocument || context : document );// If a single string is passed in and it's a single tag// just do a createElement and skip the restret = rsingleTag.exec( selector );//如果是单独标签if (ret) {//如果context是普通对象if (jQuery.isPlainObject(context)) {//之所以放在数组中,是方便后面的jQuery.merge()方法调用selector = [document.createElement(ret[1])];//调用attr方法,传入参数contextjQuery.fn.attr.call( selector, context, true );} else {selector = [ doc.createElement( ret[1] ) ];}//复杂HTML的处理方法} else {ret = jQuery.buildFragment( [ match[1] ], [ doc ] );selector = ( ret.cacheable ? jQuery.clone(ret.fragment) : ret.fragment ).childNodes;}return jQuery.merge( this, selector );// HANDLE: $("#id")} else {elem = document.getElementById( match[2] );// Check parentNode to catch when Blackberry 4.6 returns// nodes that are no longer in the document #6963if ( elem && elem.parentNode ) {// Handle the case where IE and Opera return items// by name instead of ID//即使是documen.getElementById这样核心的方法也要考虑到浏览器兼容问题,可能找到的是name而不是idif ( elem.id !== match[2] ) {return rootjQuery.find( selector );}// Otherwise, we inject the element directly into the jQuery objectthis.length = 1;this[0] = elem;}this.context = document;this.selector = selector;return this;}// HANDLE: $(expr, $(...))//没有指定上下文,执行rootjQuery.find(),制定了上下文且上下文是jQuery对象,执行context.find()} else if ( !context || context.jquery ) {return ( context || rootjQuery ).find( selector );// HANDLE: $(expr, context)// (which is just equivalent to: $(context).find(expr)//如果指定了上下文,且上下文不是jQuery对象} else {//先创建一个包含context的jQuery对象,然后调用find方法return this.constructor( context ).find( selector );}// HANDLE: $(function)// Shortcut for document ready} else if ( jQuery.isFunction( selector ) ) {return rootjQuery.ready( selector );}//selector是jquery对象if ( selector.selector !== undefined ) {this.selector = selector.selector;this.context = selector.context;}//合并到当前jQuery对象return jQuery.makeArray( selector, this );},
其中里面调用的其他jQuery函数待后面再详细学习。
1、其中用到了两个正则表达式:
(1)quickExpr = /^(?:[^#<]*(<[\w\W]+>)[^>]*$|#([\w\-]*)$)/;
解释:?:是非捕获组的意思,非捕获组只参与匹配,但不会把匹配到的内容捕获到组里,降低了内存的占用。
[^#<]*匹配除#<以外的任意字符,且出现0次或多次
(<[\w\W]+>):
\w表示匹配字母数字、下划线,\W正好相反,这里匹配的是以字母数字下划线作为第一个字母的一个标签,比如<div>
[^>]*匹配除>之外的所有字符,且出现0次或多次,$结束,表示结束时不能为>字符
#(\w\-]*)$ #id的匹配,id只能为字母、数字、下划线和减号
(2)rsingleTag = /^<(\w+)\s*\/?>(?:<\/\1>)?$/;
解释:^<(\w+)\s*\/?>:
^<:以<开头
(\w+):匹配的字母、数字、下划线
\s*:匹配空格符0次或多次,比如可以匹配<div >这样的
\/?>:匹配/符号0次或1次,比如匹配<img />这样的
(?:<\/\1>):\1表示的是前面的(),这里指的就是(\w+),比如前面是<div>,这里就要是</div>
最后的?$表示的是此元素为截止符,要么截止在</div>,要么没有就是前面的<img >或者是<img />
到此就把所有的单独的标签的情况考虑完全了。
学以致用
<script type="text/javascript">var quickExpr = /^(?:[^#<]*(<[\w\W]+>)[^>]*$|#([\w\-]*)$)/;var rsingleTag = /^<(\w+)\s*\/?>(?:<\/\1>)?$/;var match = quickExpr.exec("abc<div>#id");if (match) {alert(RegExp.$1)}var match1 = rsingleTag.exec("<div></div>");if (match1) {alert(RegExp.$1);}</script>
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