这篇文章给大家介绍jQuery中怎么实现一个构造器，内容非常详细，感兴趣的小伙伴们可以参考借鉴，希望对大家能有所帮助。
2009-01-13发布的1.3版
init: function( selector, context ) { // Make sure that a selection was provided selector = selector || document; // 处理节点参数,直接添加属性到新实例上 if ( selector.nodeType ) { this[0] = selector; this.length = 1; this.context = selector; return this; } // 处理字符串参数 if ( typeof selector === "string" ) { // 判定是否为HTML片断还是ID var match = quickExpr.exec( selector ); if ( match && (match[1] || !context) ) { // 如果是HTML片断,转换一个由节点构造的数组 if ( match[1] ) selector = jQuery.clean( [ match[1] ], context ); // 如果是ID,则查找此元素,如果找到放进空数组中 else { var elem = document.getElementById( match[3] ); // Make sure an element was located if ( elem ){ // 处理 IE and Opera 混淆ID与NAME的bug if ( elem.id != match[3] ) return jQuery().find( selector ); var ret = jQuery( elem ); ret.context = document; ret.selector = selector; return ret; } selector = []; } } else //使用Sizzle处理其他CSS表达式,生成实例并返回 return jQuery( context ).find( selector ); // 处理函数参数，直接domReady } else if ( jQuery.isFunction( selector ) ) return jQuery( document ).ready( selector ); //处理jQuery对象参数，简单地将其两个属性赋给新实例 if ( selector.selector && selector.context ) { this.selector = selector.selector; this.context = selector.context; } //将上面得到节点数组，用setArray方法把它们变成实例的元素 return this.setArray(jQuery.makeArray(selector)); },2009-02-19发布的1.32版
init: function( selector, context ) { // Make sure that a selection was provided selector = selector || document; // 处理节点参数,直接添加属性到新实例上 if ( selector.nodeType ) { this[0] = selector; this.length = 1; this.context = selector; return this; } //处理字符串参数 if ( typeof selector === "string" ) { //判定是否为HTML片断还是ID var match = quickExpr.exec( selector ); if ( match && (match[1] || !context) ) { // 如果是HTML片断,转换一个由节点构造的数组 if ( match[1] ) selector = jQuery.clean( [ match[1] ], context ); else { var elem = document.getElementById( match[3] ); // 如果是ID,则查找此元素,如果找到放进空数组中 if ( elem && elem.id != match[3] ) return jQuery().find( selector ); //这里对1.3版做了些优化,更简洁 var ret = jQuery( elem || [] ); ret.context = document; ret.selector = selector; return ret; } } else //使用Sizzle处理其他CSS表达式,生成实例并返回 return jQuery( context ).find( selector ); // 处理函数参数，进行domReady操作 } else if ( jQuery.isFunction( selector ) ) return jQuery( document ).ready( selector ); //处理jQuery对象参数，简单地将其两个属性赋给新实例 if ( selector.selector && selector.context ) { this.selector = selector.selector; this.context = selector.context; } //这里对1.3版做了些扩展,允许传珍上元素集合(HTMLCollection)与节点集合(NodeList), //元素数组可能是我们用字符串转换过来的,也可以是用户直接传进来的 return this.setArray(jQuery.isArray( selector ) ? selector : jQuery.makeArray(selector)); },2010-01-13发布的1.4版
init: function( selector, context ) { var match, elem, ret, doc; //处理空白字符串,null,undefined参数(新增),返回一个非常纯净的实例 if ( !selector ) { return this; } // 处理节点参数,直接添加属性到新实例上 if ( selector.nodeType ) { this.context = this[0] = selector;//写法上优化 this.length = 1; return this; } //处理字符串参数 if ( typeof selector === "string" ) { // 判定是否为HTML片断还是ID match = quickExpr.exec( selector ); if ( match && (match[1] || !context) ) { //如果是HTML片断 if ( match[1] ) { //取得文档对象 doc = (context ? context.ownerDocument || context : document); // 如果是单个标签,直接使用 document.createElement创建此节点并放入数组中 ret = rsingleTag.exec( selector ); if ( ret ) { //如果后面跟着一个纯净的JS对象,则为此节点添加相应的属性或样式 if ( jQuery.isPlainObject( context ) ) { selector = [ document.createElement( ret[1] ) ]; jQuery.fn.attr.call( selector, context, true ); } else { selector = [ doc.createElement( ret[1] ) ]; } } else { //改由buildFragment来生成节点集合(NodeList) ret = buildFragment( [ match[1] ], [ doc ] ); selector = (ret.cacheable ? ret.fragment.cloneNode(true) : ret.fragment).childNodes; } } else { // 如果是ID,则查找此元素,如果找到放进空数组中 elem = document.getElementById( match[2] ); if ( elem ) { // 处理 IE and Opera 混淆ID与NAME的bug if ( elem.id !== match[2] ) { return rootjQuery.find( selector ); } //这里也做了一些优化,原来是很傻地再生成一个jQuery实例 this.length = 1; this[0] = elem; } this.context = document; this.selector = selector; return this; } // 如果字符是很简单的标签选择器,那基本没有必要走Sizzle路线,直接getElementsByTagName,很好的优化 } else if ( !context && /^\w+$/.test( selector ) ) { this.selector = selector; this.context = document; selector = document.getElementsByTagName( selector ); // 如果第二个参数不存在或者是jQuery对象,那么用它或rootjQuery调用find查找目标节点(走Sizzle路线) } else if ( !context || context.jquery ) { return (context || rootjQuery).find( selector ); // HANDLE: $(expr, context) // (which is just equivalent to: $(context).find(expr) } else { //如果第二个参数已指定为某元素节点,转为jQuery对象,走Sizzle路线 return jQuery( context ).find( selector ); } // 处理函数参数，直接domReady } else if ( jQuery.isFunction( selector ) ) { return rootjQuery.ready( selector ); } //处理jQuery对象参数，简单地将其两个属性赋给新实例 if (selector.selector !== undefined) { this.selector = selector.selector; this.context = selector.context; } //这里又做了些许修改,缘于makeArray可以接受第二个参数(可以是数组或类数组,这时相当合并操作) return jQuery.isArray( selector ) ? this.setArray( selector ) ://内部用push方法,迅速将一个普通对象变成类数组对象 jQuery.makeArray( selector, this ); },接着是广受欢迎的2010-02-13发布的1.42版
init: function( selector, context ) { var match, elem, ret, doc; // 处理空白字符串,null,undefined参数 if ( !selector ) { return this; } // 处理节点参数 if ( selector.nodeType ) { this.context = this[0] = selector; this.length = 1; return this; } // 处理body参数(新增) if ( selector === "body" && !context ) { this.context = document; this[0] = document.body; this.selector = "body"; this.length = 1; return this; } // 处理字符串参数,分七种情形： //①单个标签,带对象属性包 ---> jQuery.merge //②单个标签,不带对象属性包 ---> attr + jQuery.merge //③复杂的HTML片断 ---> buildFragment + jQuery.merge //④ID选择器,与找到的元素的ID不同 ---> getElementById + Sizzle + pushStack //⑤ID选择器,与找到的元素的ID相同 ---> getElementById + 简单属性添加 //⑥标签选择器 ---> getElementsByTagName + jQuery.merge //⑦其他CSS表达式 ---> Sizzle + pushStack if ( typeof selector === "string" ) { match = quickExpr.exec( selector ); if ( match && (match[1] || !context) ) { if ( match[1] ) { doc = (context ? context.ownerDocument || context : document); ret = rsingleTag.exec( selector ); if ( ret ) { if ( jQuery.isPlainObject( context ) ) { selector = [ document.createElement( ret[1] ) ]; jQuery.fn.attr.call( selector, context, true ); } else { selector = [ doc.createElement( ret[1] ) ]; } } else { ret = buildFragment( [ match[1] ], [ doc ] ); selector = (ret.cacheable ? ret.fragment.cloneNode(true) : ret.fragment).childNodes; } return jQuery.merge( this, selector ); } else { elem = document.getElementById( match[2] ); if ( elem ) { if ( elem.id !== match[2] ) { return rootjQuery.find( selector ); } this.length = 1; this[0] = elem; } this.context = document; this.selector = selector; return this; } } else if ( !context && /^\w+$/.test( selector ) ) { this.selector = selector; this.context = document; selector = document.getElementsByTagName( selector ); return jQuery.merge( this, selector ); } else if ( !context || context.jquery ) { return (context || rootjQuery).find( selector ); } else { return jQuery( context ).find( selector ); } // 处理函数参数，直接domReady } else if ( jQuery.isFunction( selector ) ) { return rootjQuery.ready( selector ); } //处理jQuery对象参数 if (selector.selector !== undefined) { this.selector = selector.selector; this.context = selector.context; } //无论是数组还是类数组（如NodeList），统统使用jQuery.makeArray来为实例添加新的元素 return jQuery.makeArray( selector, this ); },另附上makeArray方法与merge方法，merge方法好神奇啊
makeArray: function( array, results ) { var ret = results || []; if ( array != null ) { // The window, strings (and functions) also have 'length' // The extra typeof function check is to prevent crashes // in Safari 2 (See: #3039) if ( array.length == null || typeof array === "string" || jQuery.isFunction(array) || (typeof array !== "function" && array.setInterval) ) { push.call( ret, array ); } else { jQuery.merge( ret, array ); } } return ret; }, merge: function( first, second ) { var i = first.length, j = 0; if ( typeof second.length === "number" ) { for ( var l = second.length; j < l; j++ ) { first[ i++ ] = second[ j ]; } } else { while ( second[j] !== undefined ) { first[ i++ ] = second[ j++ ]; } } first.length = i; return first; },2011-01-23发布的1.5版，其init方法与1.42的变化不大：只有两处做了改动：
//1.42 - ret = buildFragment( [ match[1] ], [ doc ] ); - selector = (ret.cacheable ? ret.fragment.cloneNode(true) : ret.fragment).childNodes; //1.5 + ret = jQuery.buildFragment( [ match[1] ], [ doc ] ); + selector = (ret.cacheable ? jQuery.clone(ret.fragment) : ret.fragment).childNodes; //1.42 - return jQuery( context ).find( selector ); //1.5 + return this.constructor( context ).find( selector );//目的就是为了不再生成新实例2011-05-02发布的jquery1.6，变化不大，只是对HTML片断进行了更严密的判定：
// Are we dealing with HTML string or an ID? 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 = quickExpr.exec( selector ); }关于jQuery中怎么实现一个构造器就分享到这里了，希望以上内容可以对大家有一定的帮助，可以学到更多知识。如果觉得文章不错，可以把它分享出去让更多的人看到。
