IE shows record button, but it doesn't work

Using Internet Explorer, I see the record button for CodeWorld programs. Clicking it gives:

SCRIPT438: Object doesn't support property or method 'captureStream'
codeworld.js (163,9)

It looks like canvas elements don't have captureStream on IE. The UI should detect that and not offer the record button if it cannot function correctly.

Start at codeworld.js line 163, where the record action reaches the unsupported captureStream method in Internet Explorer. Check how the UI exposes the record button and add the capability check described in the issue. Done means Internet Explorer does not offer recording when captureStream is unavailable, while supported browsers retain the button.

Written by the indexing model from the issue text.