Display a by retrieving option set in a web resource

Hi,

I'm new on Dynamics 365, and I still don't succeed in retrieving my option set text/values.

I would like display the options by using a web resource searching in an option set the options available. 

But after some work, I still don't succeed. 

<script>
var attribute = Xrm.Page.getAttribute('new_optionset_prenom');
var optiontable = attribute.getOptions();
var i = 0;
	for (i in optiontable)
        {
		document.getElementById("selectForm").options[document.getElementById("selectForm").options.length] = 
                new Option(optiontable[i], i);

}
</script>

I imagined that optiontable was a table of object for every option, but I don't succeed in manipulate it.

In the end I would like to get an exemple like that : 

because my option set has some name inside.

thank you for your help !

regards