Why is it necessary to determine variables such as forceTrigger in the doWatch function when it has already been determined that the current ReactiveEffect is' Dirty '?

[catpigdog]

I have some doubts while reading the source code. Could you please help me answer them? Thank you.

In line 341, it has been determined that the current reactiveEffect is' Dirty ', indicating that the data must have changed. Why do we need additional judgment (line 347)? Is this historical legacy code?

[LinusBorg]

In line 341, it has been determined that the current reactiveEffect is' Dirty ', indicating that the data must have changed.

The effect being dirty means that one or more of the effect's reactive dependencies changed. That does not necessarily mean that the effect's result itself will change.

And in the case of watch, the first argument is the effect, the second argument is the callback (cb) - and we only want to run the callback if the effect's return value actually changed (or we need to run it regardless, i.e. when deep: true is set).

The second if-check is checking weither or not to run the callback.

Demo Playground

[catpigdog]

Sincerely thank you for your answer. After reading your example, I suddenly realized that I am not familiar with watch.😅😅

[catpigdog]

I seem to have overlooked the flush parameter😅

[catpigdog]

@LinusBorg Hello, I still have one more question. Can you continue to answer for me? Thank you very much!
At line 341, priority will be given to checking the deep and forceTrigger variables because the hasChanged function cannot determine if there has been a change inside the object, and cb will need to be executed. I am not sure if my understanding is correct?
My question is line 243, why does' shallowRef 'require a ForceTrigger?