Empty hyperscript helpers return undefined

[arlair]

I was converting over to cycle-snabbdom and I think I found a bug.

When going through my existing code bit by bit, I was testing pieces as it exploded and had an empty div that was returning undefined. You could also test with something like a br.

The issue is vTree.data.ns ends up with undefined for data. I modified that one, but then there were multiple style calls with similar issues, eg vnode.data.style, oldVnode.data.style, vnode.data.style giving:

TypeError: Cannot read property 'style' of undefined

I started trying to fix it, but got distracted (and feeling kind of deprived when I found CoffeeScript's existential operator that is not available in JavaScript). I'll try check it out again later.

[TylorS]

Hi @arlair,

Any chance you could provide me a small reproducible example?

[arlair]

I think it is produceable just by putting a:

br()

hyperscript helper in any cycle-snabbdom project. I guess I can try grab a cycle-snabbdom example from somewhere and test it.

The issue is it creates the data object as undefined. Thinking about it now, changing the initial creation to always return an at least an empty object may be nicer than checking each usage of .data

[arlair]

I think this is where it starts to go wrong, you can see data is set to empty at the top, but the next line that will run is about to set data = b, which is actually undefined.

[arlair]

I think the bug is in hyperscript-helpers here:

const node =
  h =>
    tagName =>
      (first, ...rest) => {
        if (isSelector(first)) {
          return h(tagName + first, ...rest);
        } else {
          return h(tagName, first, ...rest);
        }
      };

It doesn't seem to handle when there is no first (first parameter?). Snabbdom seems to expect it to pass just the tagName, not tagName and undefined.

[TylorS]

I think that we can work around this. https://github.com/TylorS/cycle-snabbdom/blob/master/src/hyperscript.js#L43

I think it would work better if it were

-return VNode(sel, data, children, text, undefined);
+return VNode(sel, data || {}, children || [], text, undefined);

What do you think?

[arlair]

I just queried hyperscript-helpers with an issue. My current thinking is the problem is best fixed there.

[arlair]

Not sure what happens with virtual-dom, if it has the same issue.

[arlair]

I made a Hyperscript Helpers pull request and it has been merged. If you update to that version (2.1.1) it seems to solve my issue, at least on my local clones.

[TylorS]

Fixed in v1.2.1

[TylorS]

Thank you for this!