外部文件中的Ajax函数

I have an ajax call. This script is working fine when I put it in one file with the form that will be loaded with the script.

$(document).ready(function () {
    $("#uploadbutton").click(function () {
        var referenceNumber = document.getElementById('referenceNumber').value;
        $.ajax({
            type: "POST",
            url: "selectReferenceOrder.php",
            data: 'referenceNumber='+referenceNumber,
            cache: false,
            //data: $('form').serialize(),
            success:function(html)
            {
                document.getElementById('outputReference').innerHTML = html;
                alert('referenceNumber');
            }
        });
    });
});

However, when I try to put it in an external file, it doesn't give me anything.

The script of this ajax is functioned as the script that will post the form into the php file.

Reference: <input type="text" id="referenceNumber" /> 
<input type="button" id="uploadbutton" value="SEARCH"/>

I have tried many ways of doing this, but it still doesn't work:

<input type="submit" value="SEARCH" onclick="collectActed()" />

function collectActed () {
    var referenceNumber = document.getElementById('referenceNumber').value;
    $.ajax({
        type: "POST",
        url: "selectReferenceOrder.php",
        data: 'referenceNumber='+referenceNumber,
        cache: false,
        success:function(html) {
            document.getElementById('outputReference').innerHTML = html;
        }
    });
}

Please, help.

Following code works well:

<html>
<head>
        <title>Ajax Search</title>
        <script src="http://ajax.googleapis.com/ajax/libs/jquery/1.11.1/jquery.min.js"></script>
        <script type="text/javascript">
            function searchFor(suchbegriff) {
                var xmlHttp = null;
                // Mozilla, Opera, Safari sowie Internet Explorer 7
                if (typeof XMLHttpRequest != 'undefined') {
                    xmlHttp = new XMLHttpRequest();
                }
                if (!xmlHttp) {
                    // Internet Explorer 6 und älter
                    try {
                        xmlHttp = new ActiveXObject("Msxml2.XMLHTTP");
                    } catch (e) {
                        try {
                            xmlHttp = new ActiveXObject("Microsoft.XMLHTTP");
                        } catch (e) {
                            xmlHttp = null;
                        }
                    }
                }
                // If object has been created       
                if (xmlHttp) {
                    var url = "search.php";
                    var params = "search=" + search;

                    xmlHttp.open("POST", url, true);

                    //Headerinformatio for POST request
                    xmlHttp.setRequestHeader("Content-type", "application/x-www-form-urlencoded");
                    xmlHttp.setRequestHeader("Content-length", params.length);
                    xmlHttp.setRequestHeader("Connection", "close");

                    xmlHttp.onreadystatechange = function () {
                        if (xmlHttp.readyState == 4) {
                            // Zurückgeliefertes Ergebnis wird in den DIV "ergebnis" geschrieben
                            document.getElementById("result").innerHTML = xmlHttp.responseText;
                        }
                    };
                    xmlHttp.send(params);
                }
            }
        </script>
        <script>
$(document).ready(function(){
  $("input").click(function(){
    $("div").load("search.php");
  });
});
</script>
    </head>
    <body>
        <input type="text" onkeyup="searchFor(this.value);"/>
        <div id="search"></div>
    </body>
</html>