reactjs / reactjs/react.dev

Confusing setState() documentation

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#715 8 comentarios 0 reacciones 0 asignados Ver en GitHub

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Descripción

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recommend to not read from this.state directly because the calls to setState() could be batched and this.state has an outdated value but on the other side it recommends to call setState() only when the new state differs from the old state. But how can I check if the state differs when it could be potentially outdated?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

Comienza con la documentación enlazada de setState() y los ejemplos de este issue; después, verifica cómo se describen las funciones updater, el batching y el renderizado de nuevo. Se considera terminado cuando la documentación resuelve claramente la contradicción aparente y explica cómo evitar un renderizado de nuevo innecesario cuando se cumple la condición.

Escrito por el modelo de indexación a partir del texto del issue.

Evaluación

Stack tecnológico
javascript, react
Área
documentation
Tipo de issue
Documentación
Dificultad
4/5
Tiempo estimado
3-5 días
Estado de actividad
Estancado
Claridad
Necesita aclaración
Aptitud para principiantes
35/100

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