jQuery对象初始化的传参方式

　　jQuery.fn = jQuery.prototype = {

　　constructor: jQuery,

　　init: function( selector, context, rootjQuery ) {

　　var match, elem, ret, doc;

　　// 处理$(""), $(null), $(undefined), $(false)这几种参数,直接返回this

　　if ( !selector ) {

　　return this;

　　}

　　// 当传参selector为DOM结点时,将context置为selector

　　if ( selector.nodeType ) {

　　this.context = this[0] = selector;

　　this.length = 1;

　　return this;

　　}

　　// Handle HTML strings

　　// 当传入的selector参数为字符串时,

　　if ( typeof selector === "string" ) {

　　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 check

　　match = [ null, selector, null ];

　　} else {

　　match = rquickExpr.exec( selector );

　　}

　　// Match html or make sure no context is specified for #id

　　if ( match && (match[1] || !context) ) {

　　// HANDLE: $(html) -> $(array)

　　if ( match[1] ) {

　　context = context instanceof jQuery ? context[0] : context;

　　doc = ( context && context.nodeType ? context.ownerDocument || context : document );

　　// scripts is true for back-compat

　　selector = jQuery.parseHTML( match[1], doc, true );

　　if ( rsingleTag.test( match[1] ) && jQuery.isPlainObject( context ) ) {

　　this.attr.call( selector, context, true );

　　}

　　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 #6963

　　if ( elem && elem.parentNode ) {

　　// Handle the case where IE and Opera return items

　　// by name instead of ID

　　if ( elem.id !== match[2] ) {

　　return rootjQuery.find( selector );

　　}

　　// Otherwise, we inject the element directly into the jQuery object

　　this.length = 1;

　　this[0] = elem;

　　}

　　this.context = document;

　　this.selector = selector;

　　return this;

　　}

　　// HANDLE: $(expr, $(...))

　　} else if ( !context || context.jquery ) {

　　return ( context || rootjQuery ).find( selector );

　　// HANDLE: $(expr, context)

　　// (which is just equivalent to: $(context).find(expr)

　　} else {

　　return this.constructor( context ).find( selector );

　　}

　　// HANDLE: $(function)

　　// Shortcut for document ready

　　// 当selector为function时相当于$(document).ready(selector);

　　} else if ( jQuery.isFunction( selector ) ) {

　　return rootjQuery.ready( selector );

　　}

　　// 当selector参数为{selector:'#id', context:document}之类时,重置属性selector和context

　　if ( selector.selector !== undefined ) {

　　this.selector = selector.selector;

　　this.context = selector.context;

　　}

　　return jQuery.makeArray( selector, this );

　　}

　　};