Is there a way to set a DB Table variable programmatically in JavaScript?

Research the DDT object and associated "driver" methods.  Basically, the variable type of DB Table that you find in Project, Project Suite, and Keyword Test variables are a UI way of creating this DDT object type.  

So, for example, if you want to have a DB Table of data in an excel spreadsheet and be able to, on the fly, create that variable, you COULD do...

function getExcelData(excelFilePath, sheetName) {
    return DDT.ExcelDriver(excelFilePath, sheetName, true);
}

Running that function with the necessary data will create such a driveable object.

Then, TECHNICALLY what you could do is create a variable that has a type "Object" and assign the result of that function to it.  Like so.

function getExcelData(excelFilePath, sheetName) {
    return DDT.ExcelDriver(excelFilePath, sheetName, true);
}

function foo3() {
    Project.Variables.dbObject = getExcelData('C:\\Source\\Sandbox\\JavaScriptProject\\Script\\Book1.xlsx', 'DataSheet1');
    while (!Project.Variables.dbObject.EOF()){
        Log.Message(Project.Variables.dbObject.Value('Value1'));
        Log.Message(Project.Variables.dbObject.Value('Value2'));
        Project.Variables.dbObject.Next();
    }
    DDT.CloseDriver(Project.Variables.dbObject.Name);

}