In Brilliant R apps, how can I delay the firing of reactive?

I have it selectizeInput

in my application Shiny

. It is in multiple choice mode, so the user can specify multiple options.

However, reactive items that depend on selectizeInput

fire every time a selection is added. Suppose the user intends to select A

, B

and C

. Currently my application will do this costly computation to select A

, A, B

and A, B, C

when only the latter is required.

The best way I can work out is to delay the launch selectizeInput

by a second or so, so that the user can enter all the options. Each new selection must set a timer for 1 second. I know I Shiny

provide a command invalidateLater

, but this causes jet fire to fire once now and once later.

How can I only react to fire just once?