JAVASCRIPT

alert by code stackoverflow

<script language="javascript" type="text/javascript">
alert('This is what an alert message looks like.');
</script>

function showAlert() {
    var country = "Fiji";
    var city = "Suva";
    alert('The city of ' + city + ' is located in ' + country + '.');
}

<input type="button" value="Click Here" onClick="showAlert();">