returning xmlhttp responseText from function as return [duplicate]

Question

This question already has answers here:

How do I return the response from an asynchronous call? (36 answers)

im new in javascript and php , my goal is :RETURN string from xmlhttp responseText to a function return value.So i can use it with innerText or innerHTML method. the html code :

<script>
function loadXMLDoc(myurl){
    var xmlhttp;
    if (window.XMLHttpRequest){
        xmlhttp=new XMLHttpRequest();}
    else{
        xmlhttp=new ActiveXObject("Microsoft.XMLHTTP");}

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

    xmlhttp.open("GET",myurl,true);
    xmlhttp.send();
}
</script>

Answer 1

You can't.

Neither runs the code syncronous, nor would you return anything to loadXMLDoc but to the anonymous function which is the onreadystatechange handler.

Your best shot is to pass a callback function.

function loadXMLDoc(myurl, cb){
   var xmlhttp;
   if (window.XMLHttpRequest){
       xmlhttp=new XMLHttpRequest();}
   else{
       xmlhttp=new ActiveXObject("Microsoft.XMLHTTP");}

    xmlhttp.onreadystatechange=function(){
        if (xmlhttp.readyState==4 && xmlhttp.status==200){
            if( typeof cb === 'function' )
                cb(xmlhttp.responseText);
        }
    }

   xmlhttp.open("GET",myurl,true);
   xmlhttp.send();

}

And then call it like

loadXMLDoc('/foobar.php', function(responseText) {
    // do something with the responseText here
});

Answer 2

Just return the responseText property or assign its value to a variable in closure.

Returning a value:

<script>
    function loadXMLDoc(myurl) {
        var xmlhttp;
        if (window.XMLHttpRequest) {
            xmlhttp = new XMLHttpRequest();
        } else {
            xmlhttp = new ActiveXObject("Microsoft.XMLHTTP");
        }

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

        xmlhttp.open("GET", myurl, true);
        xmlhttp.send();
        return xmlhttp.onreadystatechange();
    }
</script>

Using a closure:

<script>
    var myValue = "",
        loadXMLDoc = function (myurl) {
            var xmlhttp;
            if (window.XMLHttpRequest) {
                xmlhttp = new XMLHttpRequest();
            } else {
                xmlhttp = new ActiveXObject("Microsoft.XMLHTTP");
            }

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

            xmlhttp.open("GET", myurl, true);
            xmlhttp.send();
            myValue = xmlhttp.onreadystatechange();
        };
</script>