强大的Jquery构造器$的实现方法

使用Jquery我们不得不用的一个符号是“$”，这个美元符号在Jquery中可以说功能是非常的强大。它可以按照我们的意愿选择任意的HTML标签元素。到目前来说，Jquery构造器$的版本已经到了Jquery1.6。下面我们具体来研究下最后欢迎的Jquery1.42的版本以及后续版本。

广受欢迎的2010-02-13发布的1.42版代码：

init: function( selector, context ) {
var match, elem, ret, doc;
// 处理空白字符串,null,undefined参数
if ( !selector ) {
return this;
}
// 处理节点参数
if ( selector.nodeType ) {
this.context = this[0] = selector;
this.length = 1;
return this;
}
// 处理body参数(新增)
if ( selector === "body" && !context ) {
this.context = document;
this[0] = document.body;
this.selector = "body";
this.length = 1;
return this;
}
// 处理字符串参数,分七种情形：
//①单个标签,带对象属性包 ---> jQuery.merge
//②单个标签,不带对象属性包 ---> attr + jQuery.merge
//③复杂的HTML片断 ---> buildFragment + jQuery.merge
//④ID选择器,与找到的元素的ID不同 ---> getElementById + Sizzle + pushStack
//⑤ID选择器,与找到的元素的ID相同 ---> getElementById + 简单属性添加
//⑥标签选择器 ---> getElementsByTagName + jQuery.merge
//⑦其他CSS表达式 ---> Sizzle + pushStack
if ( typeof selector === "string" ) {
match = quickExpr.exec( selector );
if ( match && (match[1] || !context) ) {
if ( match[1] ) {
doc = (context ? context.ownerDocument || context : document);
ret = rsingleTag.exec( selector );
if ( ret ) {
if ( jQuery.isPlainObject( context ) ) {
selector = [ document.createElement( ret[1] ) ];
jQuery.fn.attr.call( selector, context, true );
} else {
selector = [ doc.createElement( ret[1] ) ];
}
} else {
ret = buildFragment( [ match[1] ], [ doc ] );
selector = (ret.cacheable ? ret.fragment.cloneNode(true) : ret.fragment).childNodes;
}
return jQuery.merge( this, selector );
} else {
elem = document.getElementById( match[2] );
if ( elem ) {
if ( elem.id !== match[2] ) {
return rootjQuery.find( selector );
}
this.length = 1;
this[0] = elem;
}
this.context = document;
this.selector = selector;
return this;
}
} else if ( !context && /^\w+$/.test( selector ) ) {
this.selector = selector;
this.context = document;
selector = document.getElementsByTagName( selector );
return jQuery.merge( this, selector );
} else if ( !context || context.jquery ) {
return (context || rootjQuery).find( selector );
} else {
return jQuery( context ).find( selector );
}
// 处理函数参数，直接domReady
} else if ( jQuery.isFunction( selector ) ) {
return rootjQuery.ready( selector );
}
//处理jQuery对象参数
if (selector.selector !== undefined) {
this.selector = selector.selector;
this.context = selector.context;
}
//无论是数组还是类数组（如NodeList），统统使用jQuery.makeArray来为实例添加新的元素
return jQuery.makeArray( selector, this );
},

另附上makeArray方法与merge方法，merge方法好神奇啊！

makeArray: function( array, results ) {
var ret = results || [];
if ( array != null ) {
// The window, strings (and functions) also have 'length'
// The extra typeof function check is to prevent crashes
// in Safari 2 (See: #3039)
if ( array.length == null || typeof array === "string" || jQuery.isFunction(array) || (typeof array !== "function" && array.setInterval) ) {
push.call( ret, array );
} else {
jQuery.merge( ret, array );
}
}
return ret;
},
merge: function( first, second ) {
var i = first.length, j = 0;
if ( typeof second.length === "number" ) {
for ( var l = second.length; j
2011-01-23发布的1.5版，其init方法与1.42的变化不大：只有两处做了改动：


//1.42
- ret = buildFragment( [ match[1] ], [ doc ] );
- selector = (ret.cacheable ? ret.fragment.cloneNode(true) : ret.fragment).childNodes;
//1.5
+ ret = jQuery.buildFragment( [ match[1] ], [ doc ] );
+ selector = (ret.cacheable ? jQuery.clone(ret.fragment) : ret.fragment).childNodes;
//1.42
- return jQuery( context ).find( selector );
//1.5
+ return this.constructor( context ).find( selector );//目的就是为了不再生成新实例


2011-05-02发布的jquery1.6，变化不大，只是对HTML片断进行了更严密的判定：
// Are we dealing with HTML string or an ID?
if ( selector.charAt(0) === "" && selector.length >= 3 ) {
// Assume that strings that start and end with
Jquery构造器经过不断地完善，几乎已经接近完美。 有用  |  无用 取消

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