Peek at value

[jon49]

I would like to peek at a state value without actually causing a DOM rerender. But I always want to have the latest value when the user interacts with the UI and the DOM actually needs to be updated. Is there already an existing way to do this? If not I could put in a feature request.

So, the example would be this website https://jon49.github.io/timer/van where I have a timer. If I start the timer and then update the time it shuts off the timer. It should keep going and the user can choose to stop the timer themselves.

Here's the code: https://github.com/jon49/timer/blob/1f2be3f01832e2f97e62d95bcb3be049b8bab3bf/src/app.ts#L134

An idea I had, if this feature doesn't already exist, is to have a prefix that you could use when accessing the values, e.g., data.$myValue and then the van library would know that I want to access myValue but I don't want it to affect any rendering.

[Tao-VanJS]

I think you should put the line:

let val = secondsLeft.val

inside the clause of if statement of if (state.val === "running"). This way, the change to secondsLeft will only trigger the re-rendering of DOM when state.val is "running".

[jon49]

That doesn't fix the issue, it still resets the DOM. I think because of this line. That code is called when the start button is pressed and then causes the timer to start clicking down to 0.

So, it still seems like I need to be able to peek at the values as I use them only once. I'll try and think of a different solution/work around.

[Tao-VanJS]

Ah..., I think I know what you're asking...

Basically you want the binding function inside vanX.list not being re-executed whenever there is an update to the fields of timer. If that is what you want, as a workaround, you can add the following lines at the beginning of the binding function:

Object.assign(timer, timer)

This is because in VanJS 1.3.0, a state won't be considered as a dependency of the binding function if we set the value of the state inside the binding function.

[Tao-VanJS]

Peeking seems to be a useful feature anyway. I'm considering to add it in the next VanJS and VanX release.

[Tao-VanJS]

Hi @jon49,

With the release of VanJS 1.5.0 and VanX 0.3.0. You can use the property rawVal of State objects or vanx.raw to "peek" the state value without registering the dependency.

Hope it can help your use case :-)

[jon49]

Oh, great! I'll check that and update my app to use those values. I have some time this morning to work on it so perfect timing!

[jon49]

It seems to be working fine now.