前端封装请求方法以及如何调用

function ajax(opt) {       
	opt = opt || {};       
	opt.method = opt.method.toUpperCase() || 'POST'; //请求方法       
	opt.url = opt.url || ''; //请求地址        
	opt.async = opt.async || true; //是否异步请求       
	opt.data = opt.data || null; //传输数据        
	opt.success = opt.success || function() {}; //服务器响应成功进行相应的处理       
	var xmlHttp = null;       
	if(XMLHttpRequest) {         
		xmlHttp = new XMLHttpRequest(); //服务器请求对象	       
	}       
	else {         
		xmlHttp = new ActiveXObject('Microsoft.XMLHTTP'); //兼容微软请求对象	       
	}
	var params = [];       
	for(var key in opt.data) {         
		params.push(key + '=' + opt.data[key]);       
	}       
	var postData = params.join('&');       
	if(opt.method.toUpperCase() === 'POST') { //请求方法为POST,则执行如下操作
		         
		xmlHttp.open(opt.method, opt.url, opt.async);         
		xmlHttp.setRequestHeader('Content-Type', 'application/x-www-form-urlencoded;charset=utf-8');         
		xmlHttp.send(postData);       
	}       
	else if(opt.method.toUpperCase() === 'GET') { //请求方法为GET,则执行如下操作
		         
		xmlHttp.open(opt.method, opt.url + '?' + postData, opt.async);         
		xmlHttp.send(null);       
	}        
	xmlHttp.onreadystatechange = function() {         
		if(xmlHttp.readyState == 4 && xmlHttp.status == 200) { //响应是否成功
			            
			var data = JSON.parse(xmlHttp.responseText);           
			opt.success(data);         
		}       
	};     
}

调用：