Something that’s important to recognize is that every time you call the state updater function (like the
setName function in our component), that will trigger a re-render of the component that manages that state (the
Greeting component in our example). This is exactly what we want to have happen, but it can be a problem in some situations and there are some optimizations we can apply for
useState specifically in the event that it is a problem.
In our case, we’re reading into
localStorage to initialize our state value for the first render of our
Greeting component. But after that first render, we don’t need to read into
localStorage anymore because we’re managing that state in memory now (specifically in that
name variable that React gives us each render). So reading into
localStorage every render after the first one is unnecessary. So React allows us to specify a function instead of an actual value, and then it will only call that function when it needs to–on the initial render.
In this lesson, I’ll show you how to do this and demonstrate how it works.
From the react docs: "The initialState argument is the state used during the initial render. In subsequent renders, it is disregarded." If it is disregarded, then reading from localstorage happens on the first render only, right? Or only its value is disregarded and localstorage reading is still happening on every render?
Yes, the value is disregarded, but it's not using the value that's expensive, it's determining the value to pass that's expensive.