Ok, but surely you see the difference between this very simple/straightforward "demo app" and a real webapp? Something like Zillow, Facebook, Doordash, Spotify, etc. I looked at your code and you had to write your own render loop to accomplish this which would break down if you had interactive stuff that you were rendering out (I know, I've done this before). As it stands your interactions ("New Data", "Run", "Step", "Reset") are completely separate from the rendered data. Once you start combining those it gets harder. It's still possible but you are reinventing the wheel.

For a small demo like this vanilla JS might make sense but scaling this up does not work (once your rendered HTML reaches a certain size it's jarring when it re-renders, same deal if you have interactive UI that you are rendering out) and if you need to make 10x of these demo sites you are copy/pasting a bunch of code versus leveraging a framework that handles that stuff for you. Yes, frameworks raise your "floor" of code-size but they provide an excellent foundation to build on and skills you can reuse across projects instead of them all being one-off or having to copy/paste a bunch of code.

> Ok, but surely you see the difference between this very simple/straightforward "demo app" and a real webapp? Something like Zillow, Facebook, Doordash, Spotify, etc.

Yes and no. What are those apps really doing that's fundamentally so much more complicated ? Obviously there's a lot more to their UI's and you'd need to be careful about doing full re-renders. I suspect anything that affects global page layout could become problematic. But I think it should be possible to predetermine the page layout (unless the viewport size changes, then you'd need to re-render everything, but that should be uncommon) and only re-render within div's of preset size.

> I looked at your code and you had to write your own render loop to accomplish this which would break down if you had interactive stuff that you were rendering out

You mean like generating forms/controls ?

I have some other code I'm working on that does that and also doesn't seem particularly hard. For example I'm working on a chrome extension with an options page that updates another page and the local storage as soon as a user changes an option setting.

> Yes and no. What are those apps really doing that's fundamentally so much more complicated ?

They have more views, more data, more data that needs to be kept in sync across multiple views. You cannot rerender (and inject/replace) every time the underlying data changes. It works up to a point but once you cross that rubicon it because very painful. I don't know how better to say this or explain it. I write webapps professionally and for side-projects, maintaining any of them in vanilla js would be a non-starter. I have even tried that for "smaller" webapps that "don't need a build step", it doesn't work. SCSS is vastly superior to CSS, TS is superior to JS, and templates that support things like `v-for="item of items"` or `v-if="condition"` or `@click="doTheThing"` are superior to HTML templates with event handlers, loops spitting out html, and conditional rendering of blocks.

> You mean like generating forms/controls ?

Yes. Those things make this all more complicated. I've built exactly what you have in the past and at a certain point it falls down hard. There is a noticeable lag when you change data and go to re-render. If the user is focused on an input and you re-render they lose focus unless you make sure to reset the focus after the render. If you wanted to do something like "As the user types re-render an element to show what they typed" (think example/preview, or even something like putting the name you are typing into the UI as a header) it gets really gross really fast. So you might start having smaller render areas "I'll just re-render this 1 part" but that also gets complicated very quickly and at the end of the day you are just building a worse framework without the benefit of the community.

> You cannot rerender (and inject/replace) every time the underlying data changes.

OK, so how do the frameworks do it then ?

They do pathing/differential rendering. They don't all do it the same way but one example is they build the DOM "in memory", render it out, and then when they re-render they compare they old/new html and inject only the diff. They also have built in things to make sure you don't lose focus when you add an attribute to the input (or change it in some way).

There are lighter-weight shadow dom frameworks out there (than Vue/React/Angular) so why would you want to write one yourself?

You can even avoid a shadow DOM or vDOM entirely and differentially render using the DOM itself:

https://github.com/WebReflection/domdiff

https://github.com/WebReflection/uhtml

The JS framework benchmark shows these two are among the top performers.