Why is 'onInvalidate' only called once (in observeUntilInvalid) about mobx HOT 2 CLOSED

Hi,

observeUntilInvalid is a function you will rarely use, exactly because it run only once. Generally speaking you need sideEffect to observe something.

observeUntilInvalid in the react mixin will take the output of the observed function (which is the components render function) and return it as rendering to react. But in the mean time it tracks the dependencies and waits until the function output becomes stale. Then, it doesn't recompute, but instead call reacts component.forceUpdate and dispose itself.

reacts forceUpdate function will trigger render again to update the component, and render will trigger observeUntilInvalid, so it basically 'loops' again. The reason forceUpdate is used instead of just re-evaluating render, is that invoking render directly in itself doesn't do anything. Sure, it generates some output, but its output should be injected in the lifecyce of react components, otherwise it doesn't do anything.

So instead of re-evaluating the render method, we invoke forceUpdate, which is the proper way to trigger a render in react.

These are a lot of words, I guess an image would do better ;). Just let me know if it is still unclear

from mobx.

Thx, this helps a lot!

from mobx.