On propertychange issues with text value

JavaScript
1 
<td width="150" height="100"><input type="text" name="getAmount" style="width:300px; height:80; text-align: left;" class="last_inp" value="" onpropertychange="$('advert_1').css('display', 'none'); OnPropChanged ();"></td>

like that i put an alert code so when i insert in machine 1 dollar the value=“” changes to 1 so text input shows number i tried to make alert on propertychange i mean: when text value its > = 1 then shows alert telling that value changed to 1 or 2 3 4 but now its show me alert when its 0 and 1 too i only want > = 1 what im doing wrong?

here is javascript:

 <script type="text/javascript">
        function Init () {
            var textarea = document.getElementById ("textarea");
            if (textarea.addEventListener) {    // Firefox, Opera, Google Chrome and Safari
                textarea.addEventListener ('textInput', OnTextInput, false);    // Google Chrome and Safari
            }
        }

            // Google Chrome and Safari
        function OnTextInput (event) {
            alert ("The following text has been entered: " + event.data);
        }
            // Firefox, Google Chrome, Opera, Safari from version 5
        function OnInput (event) {
            alert ("The new content: " + event.target.value);
        }
            // Internet Explorer
        function OnPropChanged () {
            if (event.propertyName.toLowerCase () == "value>==1") {
                alert ("NEW VALUE ON TOTAL FIELD: " + event.srcElement.value);
            }
        }
        
    </script>

thanks in advance