core/play-java/src/main/java/play/libs/Comet.java
public static Flow<String, ByteString, NotUsed> string(String callbackName) {
    return Flow.of(String.class)
        .map(
            str -> {
              return ByteString.fromString("'" + StringEscapeUtils.escapeEcmaScript(str) + "'");
            })
        .via(flow(callbackName));
  }
public static Flow<String, ByteString, NotUsed> string(String callbackName) {
    return Flow.of(String.class)
        .map(
            str -> {
              return ByteString.fromString("'" + StringEscapeUtils.escapeEcmaScript(str) + "'");
            })
        .via(flow(callbackName));
  }
Produces a Flow of escaped ByteString from a series of String elements. Calls out to Comet.flow
internally.

@param callbackName the javascript callback method.
@return a flow of ByteString elements.