Part 11

11.0 Part 11 (clickable)

Update component

Comment in the code which describes the method says:

‘Perform an update to a mounted component. The componentWillReceiveProps and shouldComponentUpdate methods are called, then (assuming the update isn’t skipped) the remaining update lifecycle methods are called and the DOM representation is updated. By default, this implements React’s rendering and reconciliation algorithm. Sophisticated clients may wish to override this.’

Alright… sounds reasonable.

The first thing we check if props (1) were changed, technically, the method updateComponent can be called in two different scenarios if setState was called or props were changed. If props were actually changed, then life-cycle method componentWillReceiveProps will be called. After, React re-calculate nextState (2) based on pending state queue (queue of partial state objects which we set before, in our case queue will be like [{message: “click state message”}]). Of course, in the case with just props update state will be untouched.

Well, next step, we set shouldUpdate to default value true(3). That’s actually why when shouldComponentUpdate is not specified, a component is updated by default. Then, check if it’s not force update. As you know, it’s possible to call forceUpdate from component to update it, instead of changing state or props, but, according to React official docs, using this method is bad practice. So, in a case of force update component will be updated permanently, otherwise, specified from the component method shouldComponentUpdate will be called, and shouldUpdate will be re-assigned with its result value. If it’s determined that a component should not update, React still needs to set props and state but shortcut the rest of the update.

Alright, we’ve finished Part 11.

Let’s recap how we got here. Let’s look at the scheme one more time, then remove redundant less important pieces, and it becomes this:

11.1 Part 11 simplified (clickable)

And we should probably fix spaces and alignment as well:

11.2 Part 11 simplified & refactored (clickable)

Nice. In fact, that’s all that happens here. So, we can take the essential value from Part 11 and use it for the final updating scheme:

11.3 Part 11 essential value (clickable)

And then we’re done!

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