{{jQuery源码分析}}jQuery对象初始化的多种传参数形式

jQuery对象初始化的传参方式包括：
1.$(DOMElement)
2.$('<h1>...</h1>'), $('#id'), $('.class') 传入字符串, 这是最常见的形式, 这种传参数经常也传入第二个参数context指定上下文,其中context参数可以为$(...), DOMElement
3.$(function() {}); <===> $(document).ready(function() { });
4.$({selector : '.class', context : context}) <===> $('.class', context)

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 );
}
};