mjsonrpc_send_request impossible to debug

[Stefan Ritt]

The midas library call mjsonrpc_send_request uses a promise which in principle is a good idea. The downside is that it's very hard to debug. Let's assume we have code like

      mjsonrpc_send_request(req).then(function (rpc) {
         callback(rpc);
      }).catch(function (error) {
         alert("RPC error");
      });

If anything in callback() goes bad, it throws an exception, but that exception is caught by the catch() function of the promise, and therefore the alert("RPC error") is executed. I would rather prefer that the exception is not caught and my browser stops the JS code and tells me in which line of callback() I have a problem.

[dd1]

in google-chrome, I go to "inspect->source" and check "pause on exceptions" and "pause on caught exceptions", then it does exactly what you asked for. what is your browser? K.O.

[Stefan Ritt]

Thanks, didn't know that trick. Unfortunately my chrome has several extensions, which create exceptions all the time, so I have to skip like 10 exceptions until I get to the one I want. Is there a way to paus on exceptions only in a certain file?

[dd1]

(Stefan does not know how to debug web pages. Neither do I. Also see https://stackoverflow.com/questions/1736146/why-is-exception-handling-bad). This bug is not in midas. Closing issue. K.O.

[Stefan Ritt]

I just figured out that rewriting the catch() block fixes the problem. Originally I had

mjsonrpc_send_request(req).then(function (rpc) {
         callback(rpc);
      }).catch(function (error) {
         if (error.xhr.readyState == 4 && error.xhr.status == 0)
           alert("RPC error");
      });

Now if the callback() function has a syntax or runtime error, the catch() block is called and crashes, since error.xhr is not define. In this case, the error is a simple string describing the syntax or runtime error. Changing the code to the one below fixes the problem, so the proper error is shown.

mjsonrpc_send_request(req).then(function (rpc) {
         callback(rpc);
      }).catch(function (error) {
         if (error.xhr && error.xhr.readyState == 4 && error.xhr.status == 0)
           alert("RPC error");
         else
           alert(error);
      });