PHP echo's javascript to html but java script does't work s [duplicate]

I am trying to echo a javascript along with the html button to a .html page via ajax but when i click on button console says there is no function to execute tho there is a function in the html body am not sure what is wrong my question seems to be silly but i googled a lot i dont find any proper solution

My PHP code

echo "<button type='button' onclick='alerting();'>Testing Script</button>";
echo '<script type="text/javascript">function alerting(){alert("dfdgfg");}</script>';   

Javascript

HttPRequest = false;

    if (window.XMLHttpRequest) { // Mozilla, Safari,...
        HttPRequest = new XMLHttpRequest();
        if (HttPRequest.overrideMimeType) {
            HttPRequest.overrideMimeType('text/html');
        }
        } else if (window.ActiveXObject) { // IE
        try {
            HttPRequest = new ActiveXObject("Msxml2.XMLHTTP");
            } catch (e) {
            try {
                HttPRequest = new ActiveXObject("Microsoft.XMLHTTP");
            } catch (e) {}
        }
    } 

    if (!HttPRequest) {
        return false;
    }


    var url = 'http://localhost/text.php';
    var pmeters = "tschoolid=" + encodeURI(localStorage.getItem("txtPassword1")) +
    "&tuserid=" + encodeURI(localStorage.getItem("Userid"));


    HttPRequest.open('POST',url,true);

    HttPRequest.setRequestHeader("Content-type", "application/x-www-form-urlencoded");
    HttPRequest.setRequestHeader("Content-length", pmeters.length);
    HttPRequest.setRequestHeader("Connection", "close");
    HttPRequest.send(pmeters);


    HttPRequest.onreadystatechange = function()
    {

        if(HttPRequest.readyState == 3)  // Loading Request
        {


        }

        if(HttPRequest.readyState == 4) // Return Request
        {
            var retVal = HttPRequest.responseText;

            document.getElementById("Header_section").innerHTML = retVal;       


        }


    }