Now that both have dried up I hope we can close the vault door on js and have people learn how to code again.
I've seen so many tiny packages pull in lodash for some little utility method so many times. 400 bytes of source code becomes 70kb in an instant, all because someone doesn't know how to filter items in an array. And I've also seen plenty of projects which somehow include multiple copies of lodash in their dependency tree.
Its such a common junior move. Ugh.
Experienced engineers know how to pull in just what they need from lodash. But ... most experienced engineers I know & work with don't bother with it. Javascript includes almost everything you need these days anyway. And when it doesn't, the kind of helper functions lodash provides are usually about 4 lines of code to write yourself. Much better to do that manually rather than pull in some 70kb dependency.
Not wanting to use well constructed, well tested, well distributed libraries to make code simpler and more robust is not motivated by any practical engineering concern. It's just nostalgia and fetishism.
Because javascript isn't compiled. Its distributed as source. And that means the browser needs to actually parse all that code before it can be executed. Parsing javascript is surprisingly slow.
70kb isn't much on its own these days, but it adds up fast. Add react (200kb), a couple copies of momentjs (with bundled timezone databases, of course) (250kb or something each) and some actual application code and its easy to end up with ~1mb of minified javascript. Load that into a creaky old android phone and your website will chug.
For curiosity's sake, I just took a look at reddit in dev tools. Reddit loads 9.4mb of javascript (compressed to 3mb). Fully 25% of the CPU cycles loading reddit (in firefox on my mac) were spent in EvaluateModule.
This is one of the reasons wasm is great. Wasm modules are often bigger than JS modules, but wasm is packed in an efficient binary format. Browsers parse wasm many times faster than they parse javascript.