function login_p(mail,contrasenya){
x = "dss";
alert(x);
}
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<table align="right" id=\"login\"><tr><form name="login" action="script_login.php" method=\get">
<td class="table_log">Correo Electroníco:</td>
<td><input type="text" class="imp_table_log" name="mail_login"></td>
<td class="table_log">Contraseña:</td>
<td><input type="password" class="imp_table_log" name="contrasenya_login"></td>
<td><img src="imagenes/bt_entrar.gif" width="55" style="cursor:pointer;" onclick="login_p();"></td>
</form></tr></table>
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<td class="menu" id="myElement" name="m4" onclick="login_p(document.getElementById('mail_log in').value , document.getElementById('mail_login').value);">Tu cuenta</td>
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