Need to import dependencies in js files

[jennifer-richards]

Describe the issue

Ran into a problem, fixed by #4482, where the JS debugger was unable to inspect variables. This was caused by implicitly referring to $ to invoke jQuery in the JS file. When minified / bundled by parcel, the source map was mismatched. Adding an import $ from 'jquery' at the top of the file fixed the problem.

This undoubtedly affects other source files. Would be good to go through and make the imports explicit (or otherwise resolve the bundling problem.)

Marking as minor - only affects debugging as far as I know.

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