Why can I not return responseText from an Ajax function? [duplicate]

问题

Here is part of my Ajax function. For some reason that I cannot figure out, I am able to alert() responseText but not able to return responseText. Can anybody help? I need that value to be used in another function.

http.onreadystatechange = function(){
    if( http.readyState == 4 && http.status == 200 ){
        return http.responseText;
    }
}

回答1:

You will not be able to handle the return value that you are returning from your asynchronous callback. You should handle the responseText within the callback directly, or call a helper function to handle the response:

http.onreadystatechange = function () {
    if (http.readyState == 4 && http.status == 200) {
        handleResponse(http.responseText);
    }
}

function handleResponse (response) {
    alert(response);
}

回答2:

What about :

function handleResponse (response) {
    return response;
}

which return undefined for synchrounous and asynchronous modes

回答3:

function getdata(url,callback)
{
    var xmlhttp;
    if (window.XMLHttpRequest)
      {// code for IE7+, Firefox, Chrome, Opera, Safari
      xmlhttp=new XMLHttpRequest();
      }
    else
      {// code for IE6, IE5
      xmlhttp=new ActiveXObject("Microsoft.XMLHTTP");
      }
    xmlhttp.onreadystatechange=function()
      {
      if (xmlhttp.readyState==4 && xmlhttp.status==200)
        {
         var result = xmlhttp.responseText;
         callback(result)
        }
      }
    xmlhttp.open("POST",url,true);
    xmlhttp.send();
}

send a call back function name as second arguement to this function. You can get the response text for that function. simple. But you can't directly return anything from an asynchronous call.

来源：https://stackoverflow.com/questions/3732258/why-can-i-not-return-responsetext-from-an-ajax-function

标签

javascript

ajax

return

alert

responsetext