Comment by josephg

> why is 70kb of source code a problem?

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.