Question

How do you solve performance corner cases while using context in ReactJS, Explain with example?

Answer 1

The context uses reference identity to determine when to re-render, there are some gotchas that could trigger unintentional renders in consumers when a provider’s parent re-renders.

For example, the code below will re-render all consumers every time the Provider re-renders because a new object is always created for value.

class App extends React.Component {
  render() {
    return (
      <Provider value={{ something: "something" }}>
        <Toolbar />
      </Provider>
    );
  }
}

This can be solved by lifting up the value to parent state,

class App extends React.Component {
  constructor(props) {
    super(props);
    this.state = {
      value: { something: "something" },
    };
  }

  render() {
    return (
      <Provider value={this.state.value}>
        <Toolbar />
      </Provider>
    );
  }
}