Unexpected update on app.vue caused by calling computed on mounted

[jackylam1985]

Version

2.5.17

Reproduction link

https://jsfiddle.net/je3odvk8/

Steps to reproduce

Try click "parent button" which update the parent component's data, but I don't understand why this causes app to update. But if you remove the line #32 console.log(this.childName), this won't happened.

What is expected?

Expected only updating the Parent component and Child component when data updated on the Parent.

What is actually happening?

App updated caused by a child component when having console logging the computed data

[TDSkyz]

I found the problem on this.childProp. Anything that affects this variable will trigger the updated. So I define a variable containing the value of childProp on Data line #24, and it solve the problem.

https://jsfiddle.net/je3odvk8/6/

[jackylam1985]

Thanks @TDSkyz, hmm, but this still does not make sense to me. Why calling the computed function in mounted will cause the app to be updated?

[ysj16]

In lifecycle.js lines316 , the method 'callHook', disable dep collection when invoking lifecycle hooks by 'pushTarget()', which means the dep collection will be useless in the lifecycle method. The principle of this is that when pushTarget(), the params--watcher is 'undefined', so in the lifecycle method--mounted, Dep.target is 'undefined', which means will not run dep collection.
But I've found a BUG in this method， when invoking computed in mounted，it will pushTarget a lazyWatcher and then popTarget, during the process, it will lose pre Dep.target, which should be 'undefined' and make it to be the renderWatcher, so will run dep collection and collect the child component‘s property by renderWatcher.
#9095