jQuery對象初始化的傳參方式包括：
1.$(DOMElement)
2.$('<h1>...</h1>'), $('#id'), $('.class') 傳入字符串, 這是最常見的形式, 這種傳參數(shù)經(jīng)常也傳入第二個參數(shù)context指定上下文,其中context參數(shù)可以為$(...), DOMElement
3.$(function() {}); <===> $(document).ready(function() { });
4.$({selector : '.class', context : context}) <===> $('.class', context)
jQuery.fn = jQuery.prototype = {
constructor: jQuery,
init: function( selector, context, rootjQuery ) {
var match, elem, ret, doc;
// 處理$(""), $(null), $(undefined), $(false)這幾種參數(shù),直接返回this
if ( !selector ) {
return this;
}
// 當(dāng)傳參selector為DOM結(jié)點時,將context置為selector
if ( selector.nodeType ) {
this.context = this[0] = selector;
this.length = 1;
return this;
}
// Handle HTML strings
// 當(dāng)傳入的selector參數(shù)為字符串時,
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: $(function)
// Shortcut for document ready
// 當(dāng)selector為function時相當(dāng)于$(document).ready(selector);
} else if ( jQuery.isFunction( selector ) ) {
return rootjQuery.ready( selector );
}
// 當(dāng)selector參數(shù)為{selector:'#id', context:document}之類時,重置屬性selector和context
if ( selector.selector !== undefined ) {
this.selector = selector.selector;
this.context = selector.context;
}
return jQuery.makeArray( selector, this );
}
};