Untitled

<html>
    <head>
        <title>Bem vindo</title>
        <meta charset="UTF-8">
        <meta name="viewport" content="width=device-width, initial-scale=1.0">
        <script src="js/jquery-3.1.1.min.js"></script>
		<script>
			window.onload = function(){
				var user = document.getElementById("frmUser");
				var pass = document.getElementById("frmPassword");
				document.getElementById("btnLogar").onclick = function(event)
				{
					if(user.value == "jmariano" && pass.value == "123")
					{
						alert("Bem vindo ao Sistema");
					}
					else alert("Erro ao Conectar, verifique usuario e senha");
				}
			};
        </script>
    </head>
    <body>
        <fieldset id="fltLogin">
            <form id="frmLogin">
                Login: <input type="text" id="frmUser"/><br/>
                Senha:<input type="password" id="frmPassword"/><br/><br/>
                <input type="button" id="btnLogar" value="Entrar"/>
            </form>
        </fieldset>
    </body>
</html>