I am trying to do a conditional assignment and it doesn’t work. The datafile on the screen below should have the value of attached, which is FileAttachment {name: "sample.csv"}, but it is empty? [image] [image] Test "if" on Observable

your “if” cell puts a dataflow dependency on the variables “uploaded” and “attached”. It updates if these values change. Because uploaded does not resolve until something is uploaded, the whole cell containing the “if” code is not run at all! That’s what the vertical bar on the left means (pending)…

Thanks for the explanation. The bar could have a tooltip to explain that it is waiting for resolution of uploaded, because attached is already resolved. I used the localFileInput({value: attached}) before, but decided to rewrite the logic to be more explicit. The addInputListener looks like a JavaS…

If you really want to host the if logic in its own cell then you can also do viewof uploaded = localFileInput({value: null}) which ensures that cell resolves. If either attached, or uploaded changes the if block will be reevaluated automatically by Dataflow.

I confirm this works as needed. viewof uploaded = localFileInput({value: null}) With that, the following code is reevaluated every time a new file is uploaded. datafile = { if (uploaded) { return uploaded; } else { return attached; } } But why it is different from the previous defi…

The background to views is here: Introduction to Views / Observable / Observable It is not stated there but a view with value ‘undefined’ is not considered resolved. This also hangs: viewof uploaded = localFileInput({value: undefined}) As does viewof example = html`<div>` I think it is a consc…

That’s very interesting! In regular javascript, you can still test for undefined a === undefined but it doesn’t seem to work with an unresolved cell on observable. Interesting you can test viewof value, but it’s not reactive viewof file.value === undefined

[image] radames: Interesting you can test viewof value, but it’s not reactive viewof file.value === undefined Have a look at The `.value` is a lie.🎂 (on viewof'ed inputs at least) - #2 by mootari for an explanation.

I have hit the difficulty of conditional dataflow a few times myself in other settings, so I sat down and tried to figure out how to do it cleanly even when there is no “value” get out-of-jail-card argument. [image] How to dataflow merge on Observable In this series, I will explore prog…

Using "if" on Observable

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mootari August 18, 2021, 8:22am 8

Have a look at The `.value` is a lie.🎂 (on viewof'ed inputs at least) - #2 by mootari for an explanation.

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Using "if" on Observable

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