In what circumstances do you get this warning?
For a general case, e.g. a browser, browser REST client, the answer is not append .js to the endpoints. For example:
https://rally1.rallydev.com/slm/webservice/1.43/defect/2222.js?rankAbove=/defect/3333.js&fetch=Name,FormattedID,Rank
becomes
https://rally1.rallydev.com/slm/webservice/v2.0/defect/2222?rankAbove=/defect/3333.js&fetch=Name,FormattedID,Rank
But I saw this warning when using java toolkit, when using v2.0 and '.js' was not appended anywhere.
String[] warningList;
warningList = createResponse.getWarnings();
for (int w = 0; w < warningList.length; w++){
System.out.println(warningList[w]);
}
I submitted a bug.