Filtering a sharepoint List with Javascript

Hi Guys

I am needing help with filtering a SharePoint list with JavaScript. The scenario is that I have a drop down with values that correspond to columns on a list. I would like to filter on region and state. its fine if I have a value for region and for state but when either is say an empty string or null I cant then do a filter on either of the columns. I think my logic is flawed. I was wandering if somebody could help with this.

1. These are my filters in html

<div>
state:<select id="state"><option value="Production Geoscience">Production Geoscience</option><option value="Wells">Wells</option><option value="PetroPhysics">PetroPhysics</option><option value="GeoChem">GeoChem</option></select>
region:<select id="region"><option value="Americas">Americas</option><option value="Asia">Asia</option><option value="Global">Global</option><option value="Europe">Europe</option></select><br/><table id="ContactsList"><thead><tr><th>Name</th><th>Region</th><th>Domain</th><th>Email Me</th></tr></thead><tbody id="profilePictures"></tbody></table></div>

2. And then this retrieves their userProfile information

var gtLogName = function getUserLoginName () {


		state = "";
		region = "";
		console.log(region);
		console.log(state);

      $("#profilePictures").html("");

	if(state!=""&&region!=""){

        // execute AJAX request
        $.ajax({
             url: _spPageContextInfo.webAbsoluteUrl + "/_api/web/lists/getbytitle('experts')/items?$select=supportId&$filter=Region eq'" +region+ "' and

Domain eq '" +state+"'",
            type: "GET",
            headers: { "ACCEPT": "application/json;odata=verbose" },
            success: function (data) {

	     	console.log(data);
		var dataRes = data.d.results;
		var resultid;

		 for (i=0; i< data.d.results.length; i++) {
		 resultid = dataRes[i].supportId;
		 getUsAcc(resultid);
		console.log(region);
              }
},
            error: function () {
                alert("Failed to get details");

            }
        });

		} //end if
    }


$(function(){
	$("#profilePictures").ready(gtLogName());

	$("#state").change(function(){
		$("#profilePictures").ready(gtLogName());
	});

	$("#region").change(function(){
		$("#profilePictures").ready(gtLogName());
	});



});

So if I use the dropdown values when the region and the state have values it works. but when one of the values is null I would expect it to just pull all the values for that particular one.