原生ajax封装，数据初始化，

var ajaxTool = {
	setting : {
		method : 'get',
		url : location.href,
		data : '',
		callback : function(){alert('兄弟，你忘记写回掉函数了吧')}
	},
	ajax :function(json){
		//初始化数据
		var This = this
		this.extend(this.setting,json);
		
		//创建一个xhr对象
		var   xhr = new XMLHttpRequest();
		
		//格式化数据格式 以字符串键值队的形式传递数据
		this.setting.data = this.format(this.setting.data);
		//发送请求
		if(this.setting.method == 'get'){
			this.setting.url += "?" + this.setting.data
			this.setting.data = null;
		}
		
		xhr.open(this.setting.method,this.setting.url,true);
		
		if(this.setting.method == 'post'){
			xhr.setRequestHeader('Content-Type','application/x-www-form-urlencoded');
		}
		
		//发送请求
		
		xhr.send(this.setting.data)
		
		//监听请求状态
		
		xhr.onreadystatechange = function (){
			if(xhr.readyState==4&&xhr.status==200){
				
				var result = JSON.stringify(xhr.responseText) //假设请求的是json文件
				 
				  result = JSON.parse(result);
				 
				 This.setting.callback(result);
				    
			}
		}
		
	},
	extend :function(obj1,obj2){
		for (var attr in obj2) {
			obj1[attr] = obj2[attr]
		}
	},
	format : function(data){
		var html ="";
		for (var attr in data) {
			html += attr + '=' + data[attr]+'&';
		}
		
		html = html.substring(0,html.length-1)
		return html;
	}
	
}