SolidJS•17mo ago

Make createMemo depend on unmentioned signal

I have a createMemo that depends on a list of objects

  const items = createMemo(() => props.articles.map((article) => article.id));

  const items = createMemo(() => props.articles.map((article) => article.id));

now, when I reorder that list of objects, the createMemo does not fire again, since I guess the content staid the same. Now I defined

  const [reorderTag, setReorderTag] = createSignal(0);

  const [reorderTag, setReorderTag] = createSignal(0);

that I increment each time I reorder the list. Short of

  const items = createMemo(() => {
    console.log(`reorderTag: ${reorderTag}`);
    return props.articles.map((article) => article.id)
  });

  const items = createMemo(() => {
    console.log(`reorderTag: ${reorderTag}`);
    return props.articles.map((article) => article.id)
  });

how do I make sure it refires? Making logic depend on console.log feels dirty.

15 Replies

mattasia•17mo ago

Where you set articles in your parent component ensure it's a new object i.e. setArticles([...reOrderedArticles]) You also don't need console.log You can also just discard instead const _ = reorderTag() But better yet use 'on' for explicit depend

BersaelorOP•17mo ago

thanks, did the [...list]

mattasia•17mo ago

you also could potential change equals: to false on your signal - presuming you are actually setting it and not just mutating the article array without calling setSignal - this will run the effects even if the equality check is true

BersaelorOP•17mo ago

yeah, but I don't want to run the risk of this evauluating unnecessarily

mattasia•17mo ago

with [...list] it will evaluate every single time you setArticles if [...list] is the argument, with equals: false it will evaluate every single time too, but without the allocation of a new list

bigmistqke•17mo ago

U can do createMemo(mapArray(articles, () => ...)) if you want to only run a function a single time per element. mapArray is what <For/> is using under the hood

NesCafe•17mo ago

@bersaelor how come this does not work? can you check this playground code? https://playground.solidjs.com/anonymous/70394ed3-1bc5-4810-af96-3cb72ba6f396

Solid Playground

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NesCafe•17mo ago

btw, memo-s are usually lazy. they will not call by themselves. only effects will

BersaelorOP•17mo ago

hello, what doesn't work in your playground? When I open it I see the 1 and 2 and then 1s the 3

NesCafe•17mo ago

I mean it is working. but in your first message you mentioned that in your app it was not updating memo correctly

BersaelorOP•17mo ago

in the original question of this thread the problem came fromt he fact that I did reorder the elements in an array but not in fact change the array itself. using [...list] made sure my array is re-created, at the cost of allocating a new array your playground pushed a new item on the array. My problem was that I had an array where I moved item from position 1 to 7 but left the array object intact

NesCafe•17mo ago

ah, that what I wanted - to know what change it was performed with items. maybe you can change the code in a playground to make it move 1st element to 7th index I must mention that there are two ways for modify array inside store. one is with produce helper. second is with setArticles setter by key

BersaelorOP•17mo ago

what Mattasia said above also should be kept in mind:

with [...list] it will evaluate every single time you setArticles if [...list] is the argument, with equals: false it will evaluate every single time too, but without the allocation of a new list

In my case thats not a problem, to create new arrays when users move items around

BersaelorOP•17mo ago

I used https://solid-dnd.com to let users reorder a list of items

Solid Drag & Drop

A lightweight, performant, extensible drag and drop toolkit for Solid.

NesCafe•17mo ago

oh, good. will check it tomorrow. I'm from the phone already

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Make createMemo depend on unmentioned signal