原生js实现ajax

function ajax(){

  var ajaxData = {

    type:arguments[0].type || "GET",

    url:arguments[0].url || "",

    async:arguments[0].async || "true",

    data:arguments[0].data || null,

    dataType:arguments[0].dataType || "text",

    contentType:arguments[0].contentType || "application/x-www-form-urlencoded",

    beforeSend:arguments[0].beforeSend || function(){},

    success:arguments[0].success || function(){},

    error:arguments[0].error || function(){}

  }

  ajaxData.beforeSend()

  var xhr = createxmlHttpRequest(); 

  xhr.responseType=ajaxData.dataType;

  xhr.open(ajaxData.type,ajaxData.url,ajaxData.async); 

  xhr.setRequestHeader("Content-Type",ajaxData.contentType); 

  xhr.send(convertData(ajaxData.data)); 

  xhr.onreadystatechange = function() { 

    if (xhr.readyState == 4) { 

      if(xhr.status == 200){

        ajaxData.success(xhr.response)

      }else{

        ajaxData.error()

      } 

    }

  } 

}

  

function createxmlHttpRequest() { 

  if (window.ActiveXObject) { 

    return new ActiveXObject("Microsoft.XMLHTTP"); 

  } else if (window.XMLHttpRequest) { 

    return new XMLHttpRequest(); 

  } 

}

  

function convertData(data){

  if( typeof data === 'object' ){

    var convertResult = "" ; 

    for(var c in data){ 

      convertResult+= c + "=" + data[c] + "&"; 

    } 

    convertResult=convertResult.substring(0,convertResult.length-1)

    return convertResult;

  }else{

    return data;

  }

}

用法：

ajax({

  type:"POST",

  url:"ajax.php",

  dataType:"json",

  data:{"val1":"abc","val2":123,"val3":"456"},

  beforeSend:function(){

    //some js code

  },

  success:function(msg){

    console.log(msg)

  },

  error:function(){

    console.log("error")

  }

})