js 封装ajax

闲来无事自己写一个ajax 加深对ajax请求的理解直接上代码

function ajax(opt){
    var url        = opt.url;
    var method = opt.method || 'get';
    var async    = opt.async || true;
    var type      = opt.type || 'json';
    var data      = opt.data || {};
    var succFn  = opt.succ || function(){};
    var errFn    = opt.error || function(){};
   
    //创建xhr 
    var xhr;
    if(window.XMLHttpRequest){
         xhr = new XMLHttpRequest();
    }else{
         xhr = new ActiveXObject('Microsoft.XMLHttp');
     }
    if('get' === method){
        var t = new Date().getTime();
        if(url.indexOf('?' === -1)){
             url += '?' +concatData(data) + '&ct=' + t ;
        }else{
                url += '&' +concatData(data) + '&ct=' + t ;
        }
    }
    xhr.open(method,url,async)
    if(method === 'get'){
        xhr.send(null);
    }else{
         xhr.setHeader('Content-Type','application-x-www.form-encoded') ;
        xhr.send(data);  
    }

    if(false === async){
       cb();
    }else{
       xhr.onreadystatechange = function(){
             if(xhr.readyState == 4){
                   cb();
             }
       }
    }
    
     function cb(){
          var res = xhr.responseText;
          if(type == 'json'){
                res = JSON.parse(xhr.responseText);
          }
          if(xhr.status == 200){
                succFn(res);
          }else{
                errFn(xhr.status,xhr.statusText);
          }
     }


}

//字符串拼接函数
concatData(data){
     var arr = [];
     for(var i in data){
         arr.push(i + '=' + data[i]);
     }
     return arr.join('&');
}