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Dash for R should more robustly assert that output is a named list #181
Description
Currently, app developers can write a callback as follows, which will be evaluated:
app$callback(
output("slider-output", "children"),
list(input("slider-input", "value")),
function(value) {
return(sprintf("You have chosen %s on the slider above.", value))
}
)
However, the following (confusing) error may appear in the R console if another app remains loaded within a browser tab, resulting in continued requests to the backend, even though the callback map is properly populated:
error: Couldn't find output component.
Please let us know about this error via https://github.com/plotly/dashR/issues/new
request: 127.0.0.1 - ID_127.0.0.1 [24/Feb/2020:09:04:09 -0500] "POST /_dash-update-component HTTP/1.1" 500 0 "http://127.0.0.1:8050/" "Mozilla/5.0 (Macintosh; Intel Mac OS X 10_13_4) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/79.0.3945.130 Safari/537.36"
We should probably handle this situation by adding a check to verify that a requested ID is within the callback map, and return a helpful message indicating that it does not exist when absent. This check could be performed for both the R and Python backends, as it does not currently exist for either.
Activity
[-]Dash for R should assert that `output` is a named list[/-][+]Dash for R should more robustly assert that `output` is a named list[/+]