Example of common function for all UI5 controls
<!DOCTYPE html>
<html>
<head>
<script src="https://openui5.hana.ondemand.com/resources/sap-ui-core.js" id="sap-ui-bootstrap" data-sap-ui-theme="sap_bluecrystal" data-sap-ui-libs="sap.m"></script>
<meta charset="utf-8">
<title>JS Bin</title>
<script>
var oDummy = new sap.ui.core.Control();
sap.ui.core.Control.prototype.test = function(){
alert('My Custom Function!');
}
</script>
<script>
var oButton = new sap.m.Button("btn",{text:"sample",press:function(oEvent){
oButton.test();
}});
oButton.placeAt('content');
</script>
</head>
<body>
<div id='content'>
</body>
</html>