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Clientside PreventUpdate and no_update #963
Description
It would be helpful for clientside callbacks to be able to conditionally update components. This is not supported right now (as far as I can tell). This should be pretty simple, my idea would be to define
window.dash_clientside.no_update = {};then in updateClientsideOutput just conditionally block updating by adding
if(window.dash_clientside.no_update && outputValue === window.dash_clientside.no_update)
return;Similarly we could define window.dash_clientside.PreventUpdate and allow the use of
throw window.dash_clientside.PreventUpdate;If this seems reasonable I could put together a PR.
Activity
alexcjohnson commentedon Oct 11, 2019
Good idea! Yes, I think everything you're proposing makes sense, feel free to make a PR. One thing I'd add then is that
no_updateandPreventUpdateneed to be forbidden as namespaces indash_clientside.jjaraalm commentedon Oct 12, 2019
Yes, this is what I wanted to get feedback on first. I'm not sure that
dash_clientsideis actually the best place to put these as we expect it to be modified by users. The only way I see to do this reliably is to insertno_updateandPreventUpdateas non-writable attributes after all user callbacks are loaded (practically, just insert them before invoking any callbacks), but then what do we do if a user has already defined them? I guess just gracefully proceed as ifno_updateandPreventUpdatedidn't exist, otherwise it could be a breaking change.Is there a better namespace to put these in?
alexcjohnson commentedon Oct 13, 2019
I think that’s the right place. Yes, you could argue that forbidding those two names is a breaking change, but it seems to me extremely unlikely anyone has used those as a namespace so far. I’d put a check on the Python side that errors if those namespaces are referenced, and add them to
dash_clientsideduring callback invocation.jjaraalm commentedon Oct 14, 2019
Sounds like a plan. I'll put one together shortly.
Merge pull request plotly#963 from AnnMarieW/tooltip-fix-rangeslider
Merge pull request #963 from AnnMarieW/tooltip-fix-rangeslider