TypeError: undefined does not have a method named "concat"

[daveishere]

I rolled back dash-renderer to version 0.11.0 and the errors went away. Unfortunately I use tabs throughout the app, so I can’t use that version.

@chriddyp perhaps it is a similar issue to this:

Declaring callbacks with some non-existing Inputs results in a JS error

I figured out how to solve this, but figured I’d post about it because the initial symptom was this inscrutable error in the console: Uncaught TypeError: undefined does not have a method named "concat"(…) I have an app with tabs and buttons. Some buttons appear on one tab, some buttons appear on the other. I’d set up a callback function to be able to use a dynamic number of buttons like: @app.callback(Output(OUTPUTDIV, 'children'), [Input(button_id, 'n_clicks') for button_id in …