附上源代码：
Sigma.Ajax = Sigma.$class( {

    properties : function(){return {
            method: 'post',
            jsonParamName : Sigma.AjaxDefault.paramName,
            async: true,
            urlEncoded: true,
            encoding: null, //'GBK',
            mimeType: null, //'text/html',

            beforeSend: Sigma.$empty,
            onComplete: Sigma.$empty,
            onSuccess: Sigma.$empty,
            onFailure: Sigma.$empty,
            onCancel: Sigma.$empty,

            xhr : '',
            url: '',
            data: '',
            
            paramType : 'jsonString', // jsonString queryString xml

            headers: {
                'X-Requested-With': 'XMLHttpRequest',
                'Accept': 'text/javascript, text/html, application/xml,application/json, text/xml, */*'
            },

            autoCancel: false,

            evalScripts: false,
            evalResponse: false,
            responseContentType :'',

            dataUrl : false,
        
            queryParameters : null
    };},

        
    setQueryParameters : function(queryParameters){
        this.queryParameters=queryParameters;
    },


    initialize: function(options){
        options= options || {};
        if (Sigma.$type(options,'string')){
            options={ url : options };
        }

        if (!(this.xhr = this.getXHR())) { return; }
        var _header=Sigma.$extend(this.headers,options.headers);
        Sigma.$extend(this,options);
        if (this.mimeType){
            _header['X-Response-MimeType']=this.mimeType;
        }
        this.headers = _header;
    },


    send: function(options){

        this.running = true;

        if (Sigma.$type(options,'string')){
            options={ data : options };
        }
        options = Sigma.$extend({data: this.data, url: this.url, method: this.method}, options);
        var data = options.data, url = options.url, method = String(options.method).toLowerCase();

        if (Sigma.$invoke(this,'beforeSend',[this.xhr,data])===false){
            return this;
        }

        if (this.urlEncoded && method == 'post'){
            var encoding = (this.encoding) ? '; charset=' + this.encoding : '';
            this.setHeader('Content-type','application/x-www-form-urlencoded' + encoding);
        }

        switch(Sigma.$type(data)){
            case 'object':
                if (this.paramType =='jsonString') {
                    var _data=Sigma.$json(data);
                    data = { };
                    data[this.jsonParamName]=_data;
                }
                data = Sigma.toQueryString(data);
                break;
            default:
                // do nothing;
        }


        var _queryParameters;
        if (this.queryParameters && Sigma.$type(this.queryParameters,'object')){
            _queryParameters =  Sigma.toQueryString(this.queryParameters);
        }else if (Sigma.$type(this.queryParameters,'string')){
            _queryParameters = this.queryParameters;
        }

        if (_queryParameters && Sigma.$type(data,'string')){
            data = data + '&'+ _queryParameters;
        }

        //alert(_queryParameters)
        if ( method == 'post'){
            // todo fixed url too long. err code : 122
            var idx= url.indexOf('?');
            if (idx>=0){
                data=url.substring(idx+1)+'&'+data;
                url=url.substring(0,idx);
            }

        }else if (data && ( method == 'get' || this.dataUrl) ){
            url = url + (url.indexOf('?')>=0 ? '&' : '?') + data;
            data = null;
        }

        var _ajax=this;

        this.xhr.open(method.toUpperCase(), url, this.async);
        this.xhr.onreadystatechange = function(){
            return _ajax.onStateChange.apply(_ajax,arguments);
        };
        for (var key in this.headers ){
            try{
                this.xhr.setRequestHeader(key, this.headers[key]);
            }catch(e){

            }
        }
        //alert(data);
        this.xhr.send(data);
        if (!this.async) { this.onStateChange();}
        return this;
    },

    onStateChange: function(){
        if (this.xhr.readyState != 4 || !this.running) { return; }
        this.running = false;
        this.status = 0;
        try {
            this.status = this.xhr.status;
        }catch (e){

        }
        this.onComplete();
        if (this.isSuccess()){
            this._onSuccess();
        }else{
            this._onFailure();
        }
        this.xhr.onreadystatechange = Sigma.$empty;
    },

    isScript: function(){
        return (/(ecma|java)script/).test(this.getHeader('Content-type'));

    },


    isSuccess: function(){
        var status=this.xhr.status;
        return ((status >= 200) && (status < 300));
    },

    _onSuccess: function(){
        this.response = {
            'text': this.xhr.responseText,
            'xml': this.xhr.responseXML
        };
        this.onSuccess(this.response);
    },

    _onFailure: function(e){
        this.onFailure(this.xhr,e);
    },

    setHeader: function(name, value){
        this.headers[name]= value;
        return this;
    },

    getHeader: function(name){
        try{
            return this.xhr.getResponseHeader(name);
        }catch (e){
            return null;
        }
    },


    getXHR: function(){
        return (window.XMLHttpRequest) ? new XMLHttpRequest() : ((window.ActiveXObject) ? new ActiveXObject('Microsoft.XMLHTTP') : false);
    },

    cancel: function(){
        if (!this.running) { return this; }
        this.running = false;
        this.xhr.abort();
        this.xhr.onreadystatechange = Sigma.$empty;
        this.xhr = this.getXHR();
        this.onCancel();
        return this;
    }


} );

结果用到的地方提示，exception: Sigma.Ajax is not a constructor.


【 在 JavaExpert 的大作中提到: 】
: 看到了一段javascript源代码中用到了$class，这个$class是指什么？谢谢！
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