>You need to convert '\r\n' to '\n'. Where you do it depends on what else consumes the web call.
>On the server side:

response.Replace(Environment.NewLine,"\n");

On the browser end:

var result: string = alertMessage.replace('\r\n', '\n');

I tried on the server side, but the result is not what I'd like (the new lines are not properly displayed). I may try now Thierry's idea.

See the attached picture.