Category: React

If useEffect is being called twice even when we pass an empty array [] as the second argument, it typically indicates that there’s a side effect that’s causing the component to re-render.

Here are a few potential reasons and solutions:

Dependency Array Mismatch

Ensure that the dependency array ([]) is correctly passed as the second argument to useEffect. Double-check that we are not accidentally providing a non-empty array, which would cause useEffect to run whenever any of those dependencies change.

Check Component Render Triggers

Review the component code to see if there are any state updates, prop changes, or other side effects triggering a re-render. Make sure that there are no unintentional side effects updating state or props inside the component.

Check for React Strict Mode

If we are using React Strict Mode (<React.StrictMode>), it can cause double rendering of certain lifecycle methods and hooks for performance debugging purposes. Make sure that we are not seeing this behavior due to Strict Mode.

Check for Higher Order Components (HOCs) or Wrapper Components**:

If our component is wrapped with HOCs or nested within wrapper components, they might be causing additional renders.

Check for Nested Components

If the component is part of a larger component tree, ensure that parent components aren’t causing additional renders that could affect our component.

Check for Context or Global State Changes

If our component relies on context or global state changes, ensure that those changes aren’t triggering re-renders.

Check for Custom Hooks or External Libraries

If we are using custom hooks or external libraries, review their implementation to ensure they’re not causing additional renders.

By carefully reviewing our component code and considering these potential causes, we should be able to identify and resolve the issue causing useEffect to be called twice.

In React Native, we can hide the keyboard programmatically using the Keyboard module from the react-native package. Here’s how we can achieve this:

import { Keyboard } from 'react-native';

// Call this function to hide the keyboard
const dismissKeyboard = () => {
  Keyboard.dismiss();
};

// Example usage in a component
const MyComponent = () => {
  return (
    <View>
      <TextInput placeholder="Enter text" />
      <Button title="Hide Keyboard" onPress={dismissKeyboard} />
    </View>
  );
};

export default MyComponent;

In this example, pressing the button will trigger the dismissKeyboard function, which in turn calls Keyboard.dismiss() to hide the keyboard. Make sure we import the Keyboard module from 'react-native' at the top of our file.

This approach allows we to hide the keyboard programmatically, which can be useful in scenarios where we want to dismiss the keyboard when a certain action is performed, such as pressing a button or navigating away from a screen.

In React, there’s a fundamental difference between using constructor and getInitialState:

Constructor

In class components, the constructor method is a standard JavaScript constructor that gets called when a component is instantiated.

It’s used for initializing state, binding event handlers, and other setup operations.

We explicitly define the initial state within the constructor by assigning an object to this.state.

If we want to use instance properties or methods, we would typically define them within the constructor.

Example:

class MyComponent extends React.Component {
  constructor(props) {
    super(props);
    this.state = { count: 0 };
  }
  render() {
    return <div>{this.state.count}</div>;
  }
}

getInitialState

getInitialState is a method used in React’s older API, particularly in createClass syntax, which is now deprecated.

It’s used exclusively for initializing the state of a component.

When using getInitialState, we return an object representing the initial state of the component.

This method is not available in modern React versions (React 16.3 and later), and we should use the constructor for state initialization instead.

Example (using createClass, not recommended for modern React):

const MyComponent = React.createClass({
  getInitialState() {
    return { count: 0 };
  },
  render() {
    return <div>{this.state.count}</div>;
  },
});

In summary, constructor is a standard JavaScript method used for various initialization tasks, including state initialization in class components, while getInitialState is an older React API used for initializing state, particularly in createClass syntax, which is deprecated in modern React versions. For new projects and modern React components, we should use constructor for state initialization.

If we are encountering an “Attempted import error: ‘Switch’ is not exported from ‘react-router-dom’” message, it’s likely because we are trying to import the Switch component from react-router-dom, but it doesn’t exist.

Starting from React Router v6, Switch has been removed, and its functionality has been integrated into the Routes component. To achieve the same functionality as Switch from React Router v5 in React Router v6, weneed to use the Routes component with the element prop.

Here’s how we can refactor our code:

In React Router v5 we write

import { BrowserRouter as Router, Route, Switch } from 'react-router-dom';

function App() {
  return (
    <Router>
      <Switch>
        <Route path="/about" component={About} />
        <Route path="/contact" component={Contact} />
        <Route path="/" component={Home} />
      </Switch>
    </Router>
  );
}

Using React Router v6 we write

import { BrowserRouter as Router, Routes, Route } from 'react-router-dom';

function App() {
  return (
    <Router>
      <Routes>
        <Route path="/about" element={<About />} />
        <Route path="/contact" element={<Contact />} />
        <Route path="/" element={<Home />} />
      </Routes>
    </Router>
  );
}

In this example, the Routes component is used instead of Switch, and each Route component includes the element prop, which specifies the component to render for that route. Make sure our adjust our code accordingly based on our React Router version.

To specify a port to run a create-react-app based project, we can use the PORT environment variable. Here’s how we can do it:

1. Open our project’s package.json file.
2. Find the "scripts" section.
3. Modify the "start" script to include the PORT environment variable. It should look something like this:

"scripts": {
  "start": "PORT=3001 react-scripts start",
  ...
}

In this example, the port is set to 3001, but we can replace it with any port number we prefer.

Alternatively, we can specify the port directly in the command line when we run the npm start command:

PORT=3001 npm start

This will start our create-react-app based project on port 3001. Adjust the port number as needed for our project.