Also adds a custom rule to eslint. Since the recommended way of extending
eslint is to create plugins as standalone npm packages, the separate rule
is published as 'eslint-plugins-empty-returns'.
Fixes#8669.
This now shows `blueslip.error` and other JS exceptions in development
in the alert box at the top of the page. Hopefully this will make it
a lot easier to notice newly introduced JS exceptions when working on
Zulip.
Tweaked by tabbott to handle all JS errors, not just blueslip.error.
Fixes: #6155.
When in debug mode, previously an explicit `blueslip.error()` call
would not display the original stack trace of the error, making
debugging difficult.
This isn't perfect, in that it seems to display some tracebacks
multiple times, but at least the trace is available.
In a few cases the $.each was doing something imperatively that was
terser and easier to understand by using a different Underscore method,
so a few of these I rewrote.
Some code was using the fact that jQuery sets `this` in the callback to
be the item; I rewrote those to use an explicit parameter.
Some code was using $(some selector).each(callback). I converted these
to _.each($(some selector), callback).
One function, ui.process_condensing, was written to be a jQuery $.each
callback despite being in a totally different module from code using it.
I noticed this and updated the function's args.
(imported from commit bf5922a35f257c168cc09ec1d077415d6ef19a03)