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('&');}