Look for memory leaks in Emscripten heap when running refreshImage() and displaySection(). Suggested procedure for Firefox:

• bring up Developer Tools (opt-cmd-k), click Memory tab
• set Record call stacks, View: Aggregate, Group By: Inverted Call Stack
• reload this page, take Memory snapshot: astroem.js is largest at 67Mb
• click Console tab and execute:
•   doit1(N) to load images N times
•   doit1() to load images until var stop is set to 1
• each new Memory snapshot: astroem.js should still be largest at 67Mb