Both adding the parameter in JS or adding query in embeded URL work in my test.
In JS, a format as below should work, DO NOT mess the single quote and double quotes. You can add an alert to debug the passed JSON.stringified message.
oDataFilter:'CountryRegion eq "United States"'
oDataFilter: "<table>/<column> eq '<filtervalue>'"
One thing important is that <table>/<column> is case-sensitive. Make sure you've specified the correct names.