What I miss most is not the auto-bundling, but writing rules to tag emails with a label and the viewing (and archiving) everything that matched as a bundle.
Seems like all the backend that’s needed is built into gmail, what’s needed on the client is knowing which labels to display as a bundle.
Formatting dates with a format string is an anti-pattern. Format strings are too easy to get wrong and don't scale when you need to account for different locales. JavaScript's Intl functions do this correctly by providing an api that accepts a locale and options like weekday: narrow|short|long, year: numeric|2-digit, etc.
const only guards against changing the reference that it was assigned to. This won't break because info is still assigned to the same array. It doesn't matter that the array was mutated.
I think this article ignores that JavaScript's standard library has been growing in pace with new language features. The author mentions underscore as a good place to draw inspiration, but a ton of it's functionality has already been added to the language. forEach, map, reduce, filter, every, some, and others were added in ES5. ES6 brings find, includes, isArray, Object.assign and others. Promises were also added, make a library for them now unnecessary. Many of the current proposals aren't just for syntax additions to language, but to implement more standard library type of stuff (including string padding).