You're building a test suite for a React application that communicates with an external API. How can you ensure that actual API calls are not made during the test runs?
- Use a mocking library like Jest's jest.mock to mock the API calls.
- Manually disable the network connection on the test machine.
- Rewrite the API calls to return fake data during testing.
- Deploy the application to a staging environment for testing.
To ensure that actual API calls are not made during test runs, you can use a mocking library like Jest's jest.mock to mock the API calls. This allows you to replace the real API calls with mocked responses, enabling controlled and predictable testing without hitting external services. Manually disabling the network connection or deploying to a staging environment is not practical or recommended for unit testing. Rewriting API calls to return fake data can be done through mocking, which is a more effective approach.
If you need to render a child into a different DOM node, outside of the parent DOM hierarchy, you would use a React Portal.
- Bridge
- Gateway
- Passage
- Portal
When you need to render a child component into a different DOM node, outside of the parent DOM hierarchy, React Portals are the appropriate choice. They act as a bridge or gateway to render content in a different place in the DOM while maintaining React's component structure and functionality.
You have a component deep inside a layout but need to ensure that a modal opened from this component renders directly under the body tag, ensuring it's not affected by the CSS of parent containers. Which approach would you take in React?
- React Fragments
- React Portals
- React Redux
- React Router
To ensure that a modal renders directly under the body tag and is not affected by parent CSS, you should use React Portals. Portals allow you to render a component at a different DOM location, making it appear outside the DOM hierarchy of parent containers, thus avoiding any CSS interference. This is commonly used for modals and overlays.
The MobX ________ function ensures that a function is derived from the current state but doesn't cause side effects.
- action
- computed
- mutation
- observable
The MobX computed function ensures that a function is derived from the current state but doesn't cause side effects. Computed properties are derived values in MobX that are automatically kept in sync with the state they depend on. They are read-only and automatically update when their dependencies change. This is crucial for ensuring predictable and efficient reactivity in MobX.
What is the primary mechanism to pass data from a parent to a child component in React?
- Context API
- Props
- Redux
- State
The primary mechanism to pass data from a parent to a child component in React is through props (short for properties). Props allow you to pass data from a parent component to a child component as read-only properties. While React provides other mechanisms like state, Redux, and Context API for managing and sharing data, props is the most direct and common method for parent-child communication.
When using dynamic imports in Webpack, the import() function returns a promise that resolves into a(n) ________.
- Array
- Module
- Object
- String
When using dynamic imports in Webpack, the import() function returns a promise that resolves into a module. This module can then be used to access the exports of the dynamically imported code. Webpack treats dynamic imports as separate chunks that are loaded on-demand, enhancing performance by reducing initial bundle size. Understanding this is crucial for handling dynamically loaded code correctly.
In large state trees, the principle that allows unchanged parts of the old state and the new state to point to the same memory locations is called ________.
- Garbage Collection
- Memory Reuse
- Referential Equality
- Structural Sharing
In large state trees, the principle that allows unchanged parts of the old state and the new state to point to the same memory locations is called Structural Sharing. This technique is essential in state management libraries like Redux to optimize memory usage and enhance performance when updating state. It doesn't involve garbage collection, memory reuse in the same sense, or referential equality as the primary goal.
In a project, you have a theme toggle button that switches between dark and light modes. Nested deeply within the component hierarchy is a button that needs to know the current theme. How can you efficiently provide the theme information to the button without prop drilling?
- Pass the theme information as a URL parameter using React Router.
- Use React's useContext hook to access the theme information from a context provider higher in the component tree.
- Use a global JavaScript variable to store and access the current theme.
- Use a third-party state management library like Mobx or Recoil to share the theme information across components.
To efficiently provide the theme information to a deeply nested button without prop drilling, you can use React's useContext hook. This hook allows you to access the theme information from a context provider higher in the component tree without passing it down as props. Using third-party libraries or URL parameters is not the most straightforward and efficient approach, and using a global JavaScript variable can lead to issues with component re-renders and isn't recommended.
What is a primary benefit of using immutable state in React applications?
- Complex debugging process.
- Improved performance.
- Increased memory usage.
- Predictable and reliable application behavior.
The primary benefit of using immutable state in React applications is that it leads to predictable and reliable application behavior. Immutable state prevents unexpected changes and side effects, making it easier to reason about how the application behaves. It does not significantly impact memory usage and, in many cases, can improve performance by enabling efficient change detection. Complex debugging is reduced due to the predictability of immutable state.
For optimal user experience, it's recommended to use Suspense and React.lazy() for components that are at least ________ in size.
- Large
- Medium
- Small
- Varying sizes
For optimal user experience, it's recommended to use Suspense and React.lazy() for components that are at least medium in size. This is because the cost of loading and displaying a smaller component dynamically might outweigh the benefits of lazy loading. However, for very large components, lazy loading is often beneficial. The exact threshold for what constitutes "medium" can vary based on the specific application and performance considerations.