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How do you integrate GraphQL in React?
To integrate GraphQL in a React application, you typically use Apollo Client, which makes it easier to work with GraphQL queries and mutations. Here's a basic guide on how to set it up: 1. Install Apollo Client and GraphQL First, you need to install the necessary libraries: npm install @apollo/clienRead more
To integrate GraphQL in a React application, you typically use Apollo Client, which makes it easier to work with GraphQL queries and mutations. Here’s a basic guide on how to set it up:
1. Install Apollo Client and GraphQL
First, you need to install the necessary libraries:
npm install @apollo/client graphql
2. Set up Apollo Client
Create an
ApolloClient
instance that connects to your GraphQL server.In this code:
ApolloClient
is configured to connect to the GraphQL endpoint.ApolloProvider
wraps your React app to provide Apollo Client to the rest of your components.3. Query Data using
useQuery
HookTo fetch data from your GraphQL server, you can use the
useQuery
hook provided by Apollo.Here:
useQuery
hook sends theGET_ITEMS
query to the server.4. Mutate Data using
useMutation
HookTo send mutations (like adding or updating data), you can use the
useMutation
hook.Here:
useMutation
is used to send theADD_ITEM
mutation.addItem
mutation is called, and the form is reset.5. Error Handling and Loading States
In both
useQuery
anduseMutation
, you can handle loading, success, and error states to ensure a smooth user experience.Summary
useQuery
to fetch data anduseMutation
to send data.What is React Testing Library?
React Testing Library (RTL) is a testing utility for React that helps developers write tests for React components in a way that mimics how users interact with the app. It encourages testing the components from the user's perspective, rather than testing implementation details. This results in more mRead more
React Testing Library (RTL) is a testing utility for React that helps developers write tests for React components in a way that mimics how users interact with the app. It encourages testing the components from the user’s perspective, rather than testing implementation details. This results in more maintainable and robust tests.
It’s often used in conjunction with Jest, a popular JavaScript testing framework, to create unit and integration tests for React applications.
Key Concepts 🔑
User-centric Testing:
React Testing Library focuses on how the app behaves and how users interact with it (e.g., clicking buttons, filling forms), rather than the internal implementation of the components. This aligns tests more closely with how the app will be used in the real world.
Simple API:
The library provides simple, easy-to-understand methods for querying elements, triggering events, and asserting behavior.
Best Practices:
RTL promotes writing tests that are less coupled to implementation details (e.g., avoiding testing internal state or specific methods). Instead, you should focus on testing the component’s behavior and output.
Common Features and Functions 🔧
render()
: Renders the component into a virtual DOM for testing.screen
: The object where you can query DOM elements, similar to how a user would interact with them.fireEvent()
: Triggers DOM events (e.g., clicks, typing).waitFor()
: Waits for an element to appear or update (useful for asynchronous tests).getBy
,queryBy
,findBy
: Different query methods for finding elements in the rendered DOM.Basic Example of React Testing Library ⚡
Suppose you have a simple
Counter
component that increments a number when a button is clicked.Counter.js
Test for Counter Component (Counter.test.js)
How This Works:
render(<Counter />)
: Renders theCounter
component into a virtual DOM.screen.getByText(/increment/i)
: Queries the DOM for a button with the text “Increment.”fireEvent.click(button)
: Simulates a click event on the button.expect(countText).toHaveTextContent('Count: 1')
: Asserts that the count text has changed to “Count: 1.”Common Query Methods 🔍
getBy
: Finds an element by its role, label, text content, or other attributes. Will throw an error if the element isn’t found.getByText('Increment')
queryBy
: Similar togetBy
, but returnsnull
if the element isn’t found instead of throwing an error.queryByRole('button')
findBy
: Asynchronously finds an element, useful when waiting for a component to load or update.findByText('Loading...')
Why Use React Testing Library? 🤔
Closer to User Behavior:
Tests are written with user interactions in mind, ensuring your components work in real-world scenarios.
Better Maintainability:
By avoiding testing implementation details (like internal state), tests are less likely to break when the internal code changes.
Simplicity:
RTL encourages simple and clear tests, which are easier to read and understand.
Widely Adopted:
RTL is the most popular testing library for React apps and is often recommended by the React community and React documentation itself.
When to Use React Testing Library 📝
Summary 📚
How does code splitting work in React?
Code splitting is the technique of splitting your JavaScript bundle into smaller chunks that can be loaded on demand. This reduces the initial load time of your app, improving performance and user experience by only loading the necessary code for a particular page or feature. In React, code splittinRead more
Code splitting is the technique of splitting your JavaScript bundle into smaller chunks that can be loaded on demand. This reduces the initial load time of your app, improving performance and user experience by only loading the necessary code for a particular page or feature.
In React, code splitting is commonly achieved through dynamic
import()
statements, which allows you to load components or libraries only when they are needed.How It Works 🔧
React makes it easy to implement code splitting by using React.lazy() for dynamic imports and Suspense for handling loading states while the code is being fetched. These features enable you to split your app into multiple bundles and only load the relevant ones when the user navigates to that part of the app.
1️⃣ Using
React.lazy()
for Code SplittingReact.lazy()
allows you to load a component only when it’s needed (i.e., when it is rendered). This reduces the initial JavaScript load.Suspense
is used to handle the loading state while the lazy-loaded component is being fetched.Example: Code Splitting with
React.lazy()
Let’s create a simple example where we split the app into multiple chunks and load them only when needed.
1. Set Up Components
Home.js
– The homepage component.About.js
– A second component, which will be lazily loaded.2. Using
React.lazy()
andSuspense
3.
About.js
ComponentKey Concepts in the Example 📚
lazy()
:The
About
component is wrapped withReact.lazy()
, meaning it will only be loaded when it’s rendered for the first time.Suspense
:Since lazy loading introduces a delay in loading the component,
Suspense
is used to display a fallback (like a loading spinner or text) while the component is being fetched.2️⃣ Dynamic Import with Routes (React Router)
Code splitting is particularly useful in single-page applications (SPAs) when you’re using routing. With React Router, you can load routes lazily.
Example with React Router
In this example:
Home
andAbout
components are lazy-loaded when the user navigates to those routes, reducing the initial bundle size.Benefits of Code Splitting 🏎️
3️⃣ Advanced: Splitting Libraries and Vendors
Another common strategy is splitting third-party libraries into separate bundles so they are cached separately. For example, React and React Router can be bundled separately from your app’s code.
React does this automatically in production by separating runtime code, vendor code, and your app code into separate chunks using tools like Webpack.
Summary 💡
React.lazy()
: Dynamically import components to split code.Suspense
: Handle the loading state while waiting for the lazy-loaded component.What are controlled vs uncontrolled components?
In React, controlled and uncontrolled components refer to how the form elements (like input fields, textareas, etc.) manage their state. 1️⃣ Controlled Components 🎮 What it is:A controlled component is one where the form element’s value is controlled by React’s state. The state is the "single sourceRead more
In React, controlled and uncontrolled components refer to how the form elements (like input fields, textareas, etc.) manage their state.
1️⃣ Controlled Components 🎮
What it is:
A controlled component is one where the form element’s value is controlled by React’s state. The state is the “single source of truth,” meaning React is fully responsible for managing the value of the input field.
How it works:
The input value is tied to a piece of state, and any change in the input updates that state via an
onChange
handler.Example:
Key Points:
2️⃣ Uncontrolled Components 🕹️
What it is:
An uncontrolled component manages its own state internally (the browser handles it). In this case, React doesn’t directly manage the form element’s value. Instead, it relies on a ref to access the current value.
How it works:
The value of the input is handled by the DOM itself. React only interacts with the component when necessary (e.g., reading its value using a
ref
).Example:
Key Points:
refs
to access the input value when needed.3️⃣ Comparison 📊
ref
)ref
ordefaultValue
onChange
)value={value} onChange={handleChange}
ref={inputRef}
4️⃣ When to Use Which? 🤔
Use Controlled Components when:
Use Uncontrolled Components when:
Summary 💡
See less
What is the difference between useEffect and useLayoutEffect?
useEffect vs. useLayoutEffect in React ⚛️ Both useEffect and useLayoutEffect are hooks used to run side effects in functional components. The key difference lies in when they run in the component lifecycle. 1️⃣ useEffect — Runs After Painting 🖼️ When it runs:After the component has rendered and theRead more
useEffect
vs.useLayoutEffect
in React ⚛️Both
useEffect
anduseLayoutEffect
are hooks used to run side effects in functional components. The key difference lies in when they run in the component lifecycle.1️⃣
useEffect
— Runs After Painting 🖼️When it runs:
After the component has rendered and the browser has painted the UI.
Use it for:
Example:
✅ Pros: Doesn’t block painting → smoother UI.
⚠️ Cons: There might be a visual flicker if DOM changes happen here.
2️⃣
useLayoutEffect
— Runs Before Painting ⚡When it runs:
Right after the DOM updates but before the browser paints the screen.
Use it for:
getBoundingClientRect
).Example:
⚡ Pros: Perfect for layout reads/writes.
⚠️ Cons: Can block painting and hurt performance if overused.
3️⃣ Quick Comparison Table: 📋
useEffect
🖼️useLayoutEffect
⚡4️⃣ When to Use Which? 🧐
useEffect
for most side effects.useLayoutEffect
only when:💡 Pro Tip: If you’re not seeing visual glitches or layout issues, stick to
See lessuseEffect
—it’s better for performance. 🚀