[zdragnar]

Separation of concerns is different from separation of languages.

PHP intermingled with HTML was bad because developers would do things like run database queries and other operations that caused side effects directly in the markup. Every templating system still has logic in it, and almost every templating system as a way to create custom helpers which are written in the host language.

Since API calls and calls to react's `setState` are asynchronous, and the rendering pipeline is synchronous, it is still obvious that you can't put code that makes an AJAX call in your html markup.

[9dev]

JSX doesn't separate languages, you're mixing HTML with TypeScript. You can absolutely do database queries in your template. What is keeping you from doing `fetch('https://side-effect.ts').then(() => doSomethingHorrible())` in your template? Or invoking an `alert()`?

[zdragnar]

You can do those things, but you're not going to capture the effect that you want. Renders happen frequently, and the render process will complete before your `fetch` resolves. As for alert, the alert will pop up immediately before the render is applied to the DOM- and will likely pop up many times more than you thought it would, assuming you're popping it up based on some state variable.

In short, you can do those things maliciously, but if you do them naively it is immediately obvious when you run the code that it's not correct.

Compare that to the original analogy to mixing raw PHP and HTML templates. Since the rendering process is blocking, you can easily stuff form handling, remote API calls, and database calls in amongst your markup, and can make it "work" even if it's not clean.

Even Laravel's blade components let you write custom components and helpers in PHP which can do all of those things from the template- you just don't see the actual SQL mixed with the HTML in the same file. The problem is still there, just now it is harder to see.