Edit in JSFiddle

;(function($) {
    function AjaxQueue(override) {
        this.override = !!override;
    }
    
    AjaxQueue.prototype = {
        
        requests: new Array(),
        
        offer: function(options) {
            var _self = this;
            
            var xhrOptions = $.extend({}, options, {
                complete: function(jqXHR, textStatus) {

                    if($.isArray(options.complete)) {
                        
                        var funcs = options.complete;
                        for(var i = 0, len = funcs.length; i < len; i++)
                            funcs[i].call(this, jqXHR, textStatus);
                    
                    } else {
                        
                        if(options.complete)
                            options.complete.call(this, jqXHR, textStatus);            
                    }
                    _self.poll();
                },
               
                beforeSend: function(jqXHR, settings) {
                   if(options.beforeSend)
                       var ret = options.beforeSend.call(this, jqXHR, settings);
                   
                   if(ret === false) {
                       _self.poll();
                       return ret;
                   }
                }
            });
            
            if(this.override) {
                this.replace(xhrOptions);
            } else {
                
                this.requests.push(xhrOptions);
        
                if(this.requests.length == 1) {
                    $.ajax(xhrOptions);
                }
            }
        },
        
        replace: function(xhrOptions) {
            var prevRet = this.peek();
            if(prevRet != null) {
                prevRet.abort();
            }
            
            this.requests.shift();
            this.requests.push($.ajax(xhrOptions));
        },
        
        poll: function() {
            if(this.isEmpty()) {
                return null;    
            }
    
            var processedRequest = this.requests.shift();
            var nextRequest = this.peek();
            if(nextRequest != null) {
                $.ajax(nextRequest);
            }
    
            return processedRequest;
        },
        
        peek: function() {
            if(this.isEmpty()) {
                return null;
            }
            
            var nextRequest = this.requests[0];
            return nextRequest;
        },
        
        isEmpty: function() {
            return this.requests.length == 0;
        }
    }
    
    var AjaxManager = {
        queue: {},
        
        createQueue: function(name, override) {
            return   this.queue[name] = new AjaxQueue(override);
        },
        
        destroyQueue: function(name) {
            if(this.queue[name]) {
                this.queue[name] = null;
                delete this.queue[name];
            }
        },
        
        getQueue: function(name) {
            return ( this.queue[name] ? this.queue[name] : null); 
        }
    };
    
    $.AM = AjaxManager;
    
    
    $.Logger = function(id) {
        this.logElem = $('#' + id).get(0);
        this.logArr = [];    
    };
    $.Logger.prototype = {
        constructor: $.Logger,
        
        append: function(comment) {
            this.logArr.push('<p>' + comment + '</p>');
        },
        
        flush: function() {
            this.logElem.innerHTML = this.logArr.join('');
        },
        
        clear: function() {
            this.logElem.innerHTML = '';
            this.logArr = [];
        }
    };
})(jQuery);

$.AM.createQueue('press', true);
var logger = new $.Logger('log');

$('#searchbox').keypress(function() {
    $.AM.getQueue('press').offer({
        url: '/echo/json/',
        type: 'post',
        data: {
            json: {
                'name': 'Andrew',
                'age' : 24  
            },
            delay: 1
        },
        error: function() {
            logger.append('ajax canceled');
        },
        success: function() {
            logger.append('ajax succeeded');
        },
        complete: function() {
            //logger.flush('ajax completed');   
        }
    });
});

$('#showbtn').click(function() {
    logger.flush();
});
$('#clearbtn').click(function() {
    logger.clear();
})

<input type="text" id="searchbox" value="" placeholder="enter your keywords" />
<input type="button" id="showbtn" value="show log" />
<input type="button" id="clearbtn" value="clear log" />
<div id="log"></div>

#searchbox {
    border-radius: 5px;
    border: 1px solid #545454;
    box-shadow: 0 0 8px rgba(0, 0, 0, .6);
    padding: 2px 1px;
    height: 20px;
    width: 220px;
}
#log {
    font-size: 10px;
}