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: $(function)    // Shortcut for document ready    // 當selector為function時相當于$(document).ready(selector);    } else if ( jQuery.isFunction( selector ) ) {      return rootjQuery.ready( selector );    }    // 當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 );  }};