How to solve the problem of Redux rendering with a personalized equality check function?

edit

If you have a problem with Redux rendering not working correctly with a personalized equality check function, there are a few steps you can take to solve this issue.

1. Check your equality function

Ensure that your equality function is working correctly and returning the expected result. You can test it by comparing two values that should be equal and two values that should not be equal to verify that it's functioning as intended.

1. Use the areEqual method

You can use the areEqual method provided by react-redux to ensure that your components are only re-rendering when necessary. This method accepts two values and returns a boolean indicating whether they are equal.

For example, if you have a selector function that is returning an object and you only want to re-render the component if certain properties of that object have changed, you can use the areEqual method like this:

import { areEqual } from 'react-redux';

function MyComponent({ myObject }) {
  // Only re-render if `myObject.foo` or `myObject.bar` have changed
  return (
    <div>
      {myObject.foo}
      {myObject.bar}
    </div>
  );
}

export default React.memo(MyComponent, areEqual);

1. Use shouldComponentUpdate

If you're using class components instead of functional components, you can use the shouldComponentUpdate method to implement your own equality check.

For example:

class MyComponent extends React.Component {
  shouldComponentUpdate(nextProps) {
    const { myObject } = this.props;
    const { myObject: nextMyObject } = nextProps;
    // Only re-render if `myObject.foo` or `myObject.bar` have changed
    return myObject.foo !== nextMyObject.foo || myObject.bar !== nextMyObject.bar;
  }

  render() {
    const { myObject } = this.props;
    return (
      <div>
        {myObject.foo}
        {myObject.bar}
      </div>
    );
  }
}

export default MyComponent;

By implementing your own shouldComponentUpdate method, you can compare the current props and state to the next ones and decide whether the component should re-render or not.

1. Use React.memo

Another way to optimize your components and avoid unnecessary re-renders is by using React.memo. This higher-order component can help you improve the performance of your functional components and apply a custom equality check function.

function MyComponent({ myObject }) {
  // Only re-render if `myObject.foo` or `myObject.bar` have changed
  return (
    <div>
      {myObject.foo}
      {myObject.bar}
    </div>
  );
}

export default React.memo(MyComponent, (prevProps, nextProps) => {
  const { myObject: prevObject } = prevProps;
  const { myObject: nextObject } = nextProps;
  // Only re-render if `myObject.foo` or `myObject.bar` have changed
  return prevObject.foo === nextObject.foo && prevObject.bar === nextObject.bar;
});

In this case, you can pass a second argument to React.memo - a function that takes two parameters, prevProps and nextProps, and returns a boolean. If the function returns true, the component will not re-render; if the function returns false, the component will be updated.

In conclusion, there are multiple ways to solve the problem of Redux rendering with a personalized equality check function. Choose the method that suits your needs and apply the best practices to optimize the performance of your React components.