web.js refactoring

[shaedrich]

Fixes #218

• use of URL/URLSearchParams
• use of the nullish coalescing operator (??)
• use of String.prototype.localeCompare()
• use of Function.prototype.bind()
• use of the dataset property
• use of early returns
• use of the classList property
• use of strict equality (===)/strict inequality (!==)
• use KeyboardEvent.code instead of deprecated KeyboardEvent.keyCode
• use fetch() instead of XMLHttpRequest
• use JSDoc

[jemc]

For this PR, I've already reviewed all your changes, so don't decompose it now...

But for future PRs, please try to keep to one "kind" of fix per PR (e.g. one PR to change var to const or let, another PR to change how URL params are handled, etc), to make it easier to review (and revert, if needed) your changes.

For this time, I think we can merge it after you remove the stray commented-out line below.

[jemc]

Heads up to anyone watching the git history: I'm going to "true merge" this one instead of "squash and merge", because the individual commit messages look like individually relevant changes with reasonable commit messages, making it easier to potentially revert parts of this PR if needed.