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<!DOCTYPE html>
<html>
<head>
<script>
function s() {
var username = document.forms["n1"]["n2"].value;
var password = document.forms["n1"]["n3"].value;
if (username != "salim") {
document.querySelector("h2").innerHTML = "the username is wrong try again !!";
return false;
}

if( password != "fadhil")
{
document.querySelector('h2').innerHTML = "the password is wrong try again!!";
return false;
}
}
</script>
</head>
<body>

<form name="n1"  action="#" onsubmit="return s()" method="post">

<h2 style="color:red;background:black;"></h2>

Name: <input type="text" name="n2" placeholder="salim"/>
password: <input type="password" name="n3" placeholder="fadhil"/>

<input type="submit" value="Submit">
</form>

</body>
</html>