[✨] useOnVisible

[GrandSchtroumpf]

Is your feature request related to a problem?

Currently useVisibleTask$ runs:

• when the element enters viewport on hard navigation (<a>)
• when the component is mounted on soft navigation (<Link>)

This means that we cannot rely on it to lazy query data for example, as it'll be trigger eagerly with soft navigation.

Describe the solution you'd like

As qwik loader already has an IntersectionObserver, I think it could trigger a callback when the element is visible.

export const Item = component$(() => {
  useVisibleTask$(() => {
    // Triggered lazily on MPA
    // Triggered eagerly on SPA
  });
  useOnVisible$(() => {
    // Triggered lazily on MPA & SPA
  });
})

Describe alternatives you've considered

Create a local hook for that, but it might be difficult to optimize.

function useOnVisibleQrl(cb: QRL<() => void>, options) {
  const ref = useSignal<HTMLElement>();
  useVisibleTask$(() => {
    const observer = new IntersectionObserver((entries) => {
      for (const entry of entries) {
        if (!entry.isIntersecting) continue;
        cb();
        obserser.disconnect();
      }
    }, options);
    return () => observer.disconnect();
  })
}
const useOnVisible$ = plicit$FirstArg(useOnVisibleQrl);

Additional context

No response

[wmertens]

Hmm I wonder if that's a bug. useVisibleTask should fire only when visible, IMHO.

Here's a repro showing visible running on mount in client:
https://qwik.builder.io/playground/#v=1.2.13&f=5VjBchJBEL3nK8ZEwxLZZYEEqC3AysEqPWhZxruBBJKpEKBgExKBs0d%2FxA%2Fwe%2FwBf8HX3TOzLFkQqiwvVlKwO9Pd0z3T8%2Fo1y0lTrVeysqbgaq48MVqZQa5g%2FLyMepvyzCxgoM%2FuGeN4ACx5pQeonN1tE1J2917WxgY7%2F7xeuz%2Fp5p2IgJ6U6NPxuP3oVcN80NP9vkfImQ9Qsz3vc0HgkO3nuILm1EszBpfEmuUUuQ%2BnH1%2B%2F%2F5TDzOqBEleyOz9KGMLMeJ6yEg%2BvrvpdWLFxBIAWFI2mepYaWCySw2V7CggfD%2FFP%2BlIKA3fcoxa5Kw4kej%2B%2Ff%2F3145tqCLtqnV0QUALUp4NG0YwpFFgN%2BgE4luoKbAbiEyRnWr%2FrJ%2BZnvM2yl5pDlf0won3dmulFo4hvN5zPL5xVMmVeZum9ODxUDSnExZbICx81eUxnk7pvItvMTpol7iVpmBwtJSbVTMkkevRIQzF9ilRY4BehWe5VCJl5ZV94jRQPSFZfySEQYnhtMziGsOST9cdQs2XsSCbB%2BkxOEwn0jCI8Is8BwkwUITCcBqjsZ%2Fw%2BgaEj5RF7KSpcgrSOYZBO5x2%2Fb9Zhauk03uAtJV8qG3nADX1JRNZZCUQIUpMY5luirDh1T%2BQKqhSGdkV7yXgrmGE4abbAYuYEUrssmC9psea%2BSiPT3Oek33e3d2kmnnZBxPZbLvWeCKCB2TQ%2F0Q8bZgfAvQ3TtMv7tj2ZJVw9UudCv73ns%2BQ8FuDW%2BXMFzFhrUI56O5Miu4VRybntjIpsptHV2z0vhfOkSMxL5XppXjwy11wPJiM9RlfTeYxcjzFC0UBDEFwMg7ubopAlv%2B2zDV8PfOKtR8W9vUBAju5V0kZE6qDX61GagFAicSIk4ehBIZ%2F0pTqotekvmfXH7Ut9B2ZxEr6Q0Qd%2For%2BAQkRWAkM0c93VV9dxpCohzNHALboTPQB0qDZaCxoZDSeamElEhB%2B8875Lo1N9GV87vQXclmQs4IGSDt9ILnxSEj0NplKppG23O4gFJ7piCzZY2fpJUS8tf%2BwWN2u61awCSzh5UU9WYNF%2BtwdBs1XxcBQpv5SyK%2FxI7MmUkWMdErNupkx1hvhZAlmWWHPeiVy2LQav5RCqGTFvv51Z8dWNxfZA33InEaEVRM4dV8phSMW1pwconPSTARCNJP1pt3OjY39bDQrEIHf6%2BP4cS61W2yWW4zWxAOp3C2WNAh%2Bv1K1UJOV0JJWMSHoX4Ul4sksw1uiqb9XdQskUt7mFWyInQ9crCczBoo8mlyGgDIDBgbF3dqVNUmhG%2Frd%2Bq177J%2F0WV5W%2F32r9Bg

[GrandSchtroumpf]

@wmertens According to mhevery this is how it's working "for now" :

Once the app is running in the client useVisibleTask executes eagerly.

From his comment

I think it can be confusing as developer might think it always execute code when the element enters the viewport.

[iamriajul]

Is there any update?

[mhevery]

We are thinking of making it lazy, but it is dependant on other features landing first.

[gioboa]

We moved this issue to qwik-evolution repo to create a RFC discussion for this.
Here is our Qwik RFC process thanks.

[wmertens]

This requires that qwikloader re-subscribes the observer when the qvisible event is pushed again. Then it's just a matter of setting the handler on the DOM like all other events.

This would also partially solve QwikDev/qwik#7757