VueJS - Invalid handler for event "click": got undefined
Got it. It was not about top level function @click . It was about @click for the element which was becoming rendered when top level click was invoked. I had a misspelling in the function name. Unfortunately, Vue is not throwing the name of the missing function and that's the reason why I could not find it because I was looking in wrong place...
I also encountered this error with "@vue/cli-service": "^3.9.0". The cause was a child component requiring a function prop, which was not being passed.
Based on this, I would suggest inspecting the child component in question (if applicable) to ensure required props are being passed:
cancel_action: { type: Function, required: true},
I have got the similar error when the click function was implemented as computed function. Problem got resolved after the function got moved as a method rather than computed. This is not an answer but just updating my observation.