reactjs / reactjs/react.dev

Confusing setState() documentation

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Description

I have a general question about setState() because the documentation about this is a little bit confusing:

I have a component with a state. This state should only be updated (re-rendered) when a condition met. If not then there is no need to re-render the component. Reading the docs about setState tells me that reading this.state right after calling setState() is a potential pitfall. Instead I should use setState with an updater function because there prevState is guaranteed to has the right value. So my first approach was:

class MyComponent extends React.Component {
  onSomething = () => {
    this.setState(prevState => {
      if (prevState.counter < 10) {
        return { counter: prevState.counter + 1 };
      }
      return prevState;
    });
  }
}

But with that approach my component always get re-rendered because setState() always forces a re-render (in the beginning I thought that when I return the same prevState object React does nothing. But I was wrong). So what else can I do to avoid re-rendering?

Again in the same doc we can read that calling setState() only when the new state differs from the previous state will avoid unnecessary re-renders. So I could re-write my code into following:

class MyComponent extends React.Component {
  onSomething = () => {
    if (this.state.counter < 10) {
      this.setState(prevState => {
        return { counter: prevState.counter + 1 };
      });
    }
  }
}

But then if (this.state.counter < 10) could have a different value than prevState.counter

So on the one side the docs recommend to not read from this.state directly because the calls to setState() could be batched and this.state has an outdated value but on the other side it recommends to call setState() only when the new state differs from the old state. But how can I check if the state differs when it could be potentially outdated?

In the end I don't know actually how to set my state and avoid a re-rerender when a condition met. Any help here would be great.

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First steps

  1. Read the whole issue, then the project's contributing guide.
  2. Comment on the issue to say you are picking it up — it saves two people doing the same work.
  3. Fork the repository and make your change on a branch.
  4. Open a pull request that references the issue number.

Research direction

Start with the linked setState() documentation and the examples in this issue, then verify how updater functions, batching, and re-rendering are described. Done means the documentation clearly resolves the apparent contradiction and explains how to avoid an unnecessary re-render when the condition is met.

Written by the indexing model from the issue text.

Assessment

Tech stack
javascript, react
Domain
documentation
Issue type
Documentation
Difficulty
4/5
Estimated time
3-5 days
Activity status
Stale
Clarity
Needs clarification
Newbie friendliness
35/100

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