las contraseñas no coinciden

[wspetrucci]

actualmente estoy validando con js.

Código Javascript:

function checkPass() {
    if (document.getElementById("pass_usuario").value == document.getElementById("confirm_pass").value)
        return true;
    else
        alert("Las contraseñas no coinciden");
    return false;
}
 

Código HTML:

<form id="nuevo_usuario" action="php/registro.php" method="POST">
            <input type="email" name="email_usuario"  placeholder="E-mail" required="" autocomplete="off" onclick="this.placeholder='';" onblur="this.placeholder=(this.placeholder=='')?'E-mail':this.placeholder;">
            <input type="password" id="pass_usuario" name="pass_usuario"  placeholder="Contrase&ntilde;a" required="" onclick="this.placeholder='';" onblur="this.placeholder=(this.placeholder=='')?'Contrase&ntilde;a':this.placeholder;">
            <input type="password" id="confirm_pass" name="confirm_pass"  placeholder="Confirmar contrase&ntilde;a" required="" onclick="this.placeholder='';" onblur="this.placeholder=(this.placeholder=='')?'Confirmar contrase&ntilde;a':this.placeholder;">
            <input type="submit" name="registrar" value="Registrar" onclick="return checkPass();">
        </form>