jQuery.fn = jQuery.prototype = {
Constructor: jQuery,
init: function(selector, context, rootjQuery) {
var match, elem, ret, doc;
​​​​ // Process the parameters $(""), $(null), $(undefined), $(false) and directly return this
           if ( !selector ) {
              return this;
}
                                                            // When the passed parameter selector is a DOM node, set the context to selector
If (selector.nodeType) {
This.context = this[0] = selector;
This.length = 1;
              return this;
}
               // Handle HTML strings
// When the incoming selector parameter is a string,
            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 );
    }
};