questions about tf2_web_republisher

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Hi everyone. Actually I'm trying to study the tf_web_republisher code, and I find some difficulties about understanding how tfClient on roslibjs works with tf2_web_republisher. It seems that TFClient just listens to TF service; it does not send a goal nor receive a result. Isn't it? if is it so, what is the diffrence between this example visualizing a urdf file and this one writing a tfclient thank you very much

-Meriem