Do m.redraw() and m.redraw.sync() actually work?

[EverettMcKay]

Mithril.js version:
using mithril: 2.2.2

I have a react background and have been using Mithril for a couple projects lately. Love the simplicity and conciseness of the code. Overall very pleased.

But with one glaring exception: I have probably tried using m.redraw() in about 20 different circumstances, and so far I'm 0 for 20. There is a state change, but redraw never shows it.

Code

To provide a bit of code, suppose I have a component that looks like this:

let state = false;
const SomeComponent= () => {
  return {
    view: () => {
      if (state) return <p>State is set</p>;
      return <p>State is not set</p>;
    },
  };
};

Expected Behavior

If clicking a button changes state (perhaps after a server call), the component should refresh and if not, m.redraw should force it, right? But it never works...and is very frustrating. Placing a breakpoint in the view function shows that the component is never rerendered, with or without the m.redraw.

By contrast, forcing a redraw with something like m.render(document.body, getBody()) works every time, but I assume is probably not a good idea. I'm using that a lot now to avoid wasting time but it seems wrong.

Question

Is there a trick to getting ordinary state changes after interaction to redraw components?

(In React, the answer to this question is to use UseState and unique keys for iterables.)

[Oscar]

Hello 🙂 One possibility might be that you're using m.render (no autoredraw) vs. m.mount (autoredraw)?
Here's an example.

[Pierre-Yves Gérardy]

@osban got there first, I was about to suggest the same.

Here's the example I cobbled together, using JSX since this is what @EverettMcKay uses. When creating a flems from scratch, you must toggle Babel for the .js file in the hamburger menu, and set the pragmas.

[EverettMcKay]

That's it. Brilliant! Thanks!

A console message that explains any futile m.redraw() calls (and what to do instead) would earn a gold star.

[Pierre-Yves Gérardy]

@EverettMcKay good point, we could emit a warning if it is called when no reactive root have been defined.