SolidJS•14mo ago

Pass every child in props.children a context of their index

I want to create a table where every cell knows its column number without passing it via props. I tried multiple things but they all either didn't work at all or returned undefined when getting the index from the context. Here is how I would like it to work:

const ColumnContext = createContext();

function Cell(props) {
  const column = useContext(ColumnContext);
  
  onMount(() => console.log(column)); // logs undefined, expected index
  
  return (
    ...
  );
}

function Row(props) {
  const resolved = children(() => props.children);
  return (
    <div>
      <For each={resolved()}>
        {(child, index) => (
          <ColumnContext.Provider value={index()}>
            {child}
          </ColumnContext.Provider>
        )} 
      </For>
    </div>
  );
}

function App() {
  return (
    <Row>
      <Cell>...</Cell>
      <Cell>...</Cell>
      <Cell>...</Cell>
    </Row>
  );
}

const ColumnContext = createContext();

function Cell(props) {
  const column = useContext(ColumnContext);
  
  onMount(() => console.log(column)); // logs undefined, expected index
  
  return (
    ...
  );
}

function Row(props) {
  const resolved = children(() => props.children);
  return (
    <div>
      <For each={resolved()}>
        {(child, index) => (
          <ColumnContext.Provider value={index()}>
            {child}
          </ColumnContext.Provider>
        )} 
      </For>
    </div>
  );
}

function App() {
  return (
    <Row>
      <Cell>...</Cell>
      <Cell>...</Cell>
      <Cell>...</Cell>
    </Row>
  );
}

Is this even possible and if so how?

14 Replies

Jasmin•14mo ago

The issue here is that children(() => props.children) resolves the children before they get put under the context provider. and there isn't really a way to resolve only "one" children to split them under multiple context providers.

florianOP•14mo ago

So the way how I wanna do it isn't possible?

REEEEE•14mo ago

You could make the cells "register" with the Row and the row increments a counter of the totals cells or saves something like the ref of the cell, and the cell can get it's index based on that info

florianOP•14mo ago

Thanks! Already kinda knew I will have to use register/unregister but I wanted to make sure I don't miss anything. This is what I'm using for now:

const RowContext = createContext();

function useRow() {
    return useContext(RowContext);
}

function Cell() {
    const row = useRow();
    const columnIndex = row.register();

    onCleanup(() => row.unregister(columnIndex()));

    return <div textContent={columnIndex()}/>;
}

function Row(props) {
    const indexes = [];

    const context = {
        register() {
            const [index, setIndex] = createSignal(indexes.length);
            indexes.push([index, setIndex]);
            return index;
        },
        unregister(columnIndex) {
            indexes.splice(columnIndex, 1);
            for (let i = columnIndex; i < indexes.length; i++) {
                indexes[i][1](prev => prev - 1);
            }
        }
    };

    return (
        <RowContext.Provider value={context} children={props.children} />
    );
}

export default function App() {
    const [cells, setCells] = createSignal(3);
    return (
        <>
            <button onClick={() => setCells(prev => prev + 1)}>Add</button>
            <button onClick={() => setCells(prev => prev - 1)}>Remove</button>
            <Row>
                <For each={Array.from({length: cells()})}>
                    {() => <Cell />}
                </For>
            </Row>
        </>
    );
}

const RowContext = createContext();

function useRow() {
    return useContext(RowContext);
}

function Cell() {
    const row = useRow();
    const columnIndex = row.register();

    onCleanup(() => row.unregister(columnIndex()));

    return <div textContent={columnIndex()}/>;
}

function Row(props) {
    const indexes = [];

    const context = {
        register() {
            const [index, setIndex] = createSignal(indexes.length);
            indexes.push([index, setIndex]);
            return index;
        },
        unregister(columnIndex) {
            indexes.splice(columnIndex, 1);
            for (let i = columnIndex; i < indexes.length; i++) {
                indexes[i][1](prev => prev - 1);
            }
        }
    };

    return (
        <RowContext.Provider value={context} children={props.children} />
    );
}

export default function App() {
    const [cells, setCells] = createSignal(3);
    return (
        <>
            <button onClick={() => setCells(prev => prev + 1)}>Add</button>
            <button onClick={() => setCells(prev => prev - 1)}>Remove</button>
            <Row>
                <For each={Array.from({length: cells()})}>
                    {() => <Cell />}
                </For>
            </Row>
        </>
    );
}

Lmk if anyone finds a better/more performant solution 🙂

bigmistqke•14mo ago

mmm, i am not sure if context will work if you want to consider re-ordering of elements and conditionals with <Show/> and the like

bigmistqke•14mo ago

but if u don't mind typescript yelling at u and going a bit hacky: https://playground.solidjs.com/anonymous/2abb0360-ba22-4e08-9a66-0bc71b53c518

Solid Playground

Quickly discover what the solid compiler will generate from your JSX template

Otonashi•14mo ago

the implementation is rough (index is an accessor) but the idea is correct, you have to delay execution of the children until you can inject the index either directly or via context in any case if you intend to use that method, https://github.com/solidjs-community/solid-primitives/tree/main/packages/jsx-tokenizer may help here's a slightly different example for reference https://playground.solidjs.com/anonymous/e0d4d0b4-7007-405b-848f-e5efdf80c26f

bigmistqke•14mo ago

ye ur right, https://playground.solidjs.com/anonymous/d18d727d-e12c-4e7c-8580-5eab1c8be582 would be better

Solid Playground

Quickly discover what the solid compiler will generate from your JSX template

bigmistqke•14mo ago

mm interesting. i don't really understand tbh how this works. i had the impression before children would just execute all functions, no matter how nested, until it got a non-function value, but mb that was an incorrect assumption. we were actually thinking of going for a simpler cast with jsx-tokenizer but never got around implementing it https://github.com/solidjs-community/solid-primitives/issues/399 i would prefer it if it got official support bc it's pretty cool u can do this kind of stuff and is a quality that sets solid apart

Otonashi•14mo ago

it ignores functions with .length != 0 is there a reason you're calling setIndex instead of simply passing the index accessor? i.e. https://playground.solidjs.com/anonymous/53013ab4-28af-4619-8be6-fe94248bf648

bigmistqke•14mo ago

True 🙏 mm i don't completely catch that, wdym? how is the length of (v) => <>{props.children}</>; != 0?

Otonashi•14mo ago

.length of a function is the number of arguments it has

bigmistqke•14mo ago

i see that's good to know! that would solve this issue too

florianOP•14mo ago

Thanks for all the help again! Think I'm pretty happy with this solution now:

import {children, createContext, createSignal, For, Show, useContext} from "solid-js";

const ColumnContext = createContext();

function useColumn() {
    return useContext(ColumnContext);
}

function Cell(props) {
    return {
        render() {
            const column = useColumn();
            return (
                <div>
                    {column()}. {props.textContent}
                </div>
            );
        }
    };
}

function Row(props) {
    const resolved = children(() => props.children);

    return (
        <div style="display: flex; column-gap: 20px">
            <For each={resolved.toArray().filter(Boolean)}>
                {(child, index) => (
                    <ColumnContext.Provider value={index}>
                        {child.render ? child.render() : child}
                    </ColumnContext.Provider>
                )}
            </For>
        </div>
    );
}

export default function App() {
    const [cells, setCells] = createSignal(3);
    const [showCell, setShowCell] = createSignal(false);
    return (
        <>
            <button onClick={() => setCells(prev => prev + 1)}>Add</button>
            <button onClick={() => setCells(prev => prev - 1)}>Remove</button>
            <button onClick={() => setShowCell(prev => !prev)}>{showCell() ? "Hide" : "Show"}</button>
            <Row>
                <Show when={showCell()}>
                    <Cell textContent="show" />
                </Show>
                <For each={Array.from({length: cells()})}>
                    {() => <Cell textContent="for" />}
                </For>
            </Row>
        </>
    );
}

import {children, createContext, createSignal, For, Show, useContext} from "solid-js";

const ColumnContext = createContext();

function useColumn() {
    return useContext(ColumnContext);
}

function Cell(props) {
    return {
        render() {
            const column = useColumn();
            return (
                <div>
                    {column()}. {props.textContent}
                </div>
            );
        }
    };
}

function Row(props) {
    const resolved = children(() => props.children);

    return (
        <div style="display: flex; column-gap: 20px">
            <For each={resolved.toArray().filter(Boolean)}>
                {(child, index) => (
                    <ColumnContext.Provider value={index}>
                        {child.render ? child.render() : child}
                    </ColumnContext.Provider>
                )}
            </For>
        </div>
    );
}

export default function App() {
    const [cells, setCells] = createSignal(3);
    const [showCell, setShowCell] = createSignal(false);
    return (
        <>
            <button onClick={() => setCells(prev => prev + 1)}>Add</button>
            <button onClick={() => setCells(prev => prev - 1)}>Remove</button>
            <button onClick={() => setShowCell(prev => !prev)}>{showCell() ? "Hide" : "Show"}</button>
            <Row>
                <Show when={showCell()}>
                    <Cell textContent="show" />
                </Show>
                <For each={Array.from({length: cells()})}>
                    {() => <Cell textContent="for" />}
                </For>
            </Row>
        </>
    );
}

This way its also pretty easy to just remove the context stuff and make the index available to the cell via putting it in the render() args instead

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Pass every child in props.children a context of their index

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