search

numbas / Numbas

A completely browser-based e-assessment/e-learning system, with an emphasis on mathematics
http://www.numbas.org.uk
Apache License 2.0
207 stars 122 forks source link

Numbas exam fails to open with TypeError: "tok" of null #684

Closed oscarsiles closed 4 years ago

oscarsiles commented 4 years ago

I have had a student receive the following error on one of their attempts, which does not allow the attempt to be run by either themselves or a teacher. Their scores and JSON data can be seen just fine in the LTI tool.

TypeError: Cannot read property 'tok' of null at Object.jme.findvars (xxx/scripts.js:21064:13) at c. (xxx/scripts.js:28766:36) at Function.Uc (xxx/scripts.js:22771:20) at Function.Vc (xxx/scripts.js:22770:299) at Function.U (xxx/scripts.js:22770:126) at xxx/scripts.js:22769:462 at xxx/scripts.js:22735:297

Not quite sure what might have caused this, to be honest, as the student was saving and returning to the exam a handful of times without issues. It does appear the student was able to submit a blank answer for one of the questions during the session that caused the issue to appear.

Am happy to provide additional information if needed

christianp commented 4 years ago

Can you give a link to the exam in the Numbas editor please?

christianp commented 4 years ago

Didn't meant to close this! Looking at the error message, I made a guess that somehow Numbas.jme.findvars was being passed a null value, which I suppose could happen if the student had submitted a blank answer. I've added a line to catch this safely.

Now I'll try to work out how the student submitted nothing.

christianp commented 4 years ago

OK, I worked out how to reproduce the problem, and I believe I've fixed it. In order for this student to continue their attempt, you'd have to update the exam package. I've just added an option to the LTI tool to make existing attempts use the new version when you replace the exam package; your admin will need to update your installation of the LTI tool to version 2.6.

oscarsiles commented 4 years ago

That is excellent, thank you! Thankfully it was only 1 student with the issue (out of a few hundred), but going forward it will be nice to avoid it altogether.