When mocking a specific function implementation with Jest, you would use the method ________ on the mock.
- mockImplementation
- getMockFunction
- functionMock
- mockedFunction
In Jest, when you want to mock a specific function implementation, you would use the mockImplementation method on the mock. This allows you to define custom behavior for the mocked function, such as returning specific values or throwing errors. The other options are not the correct method for this purpose in Jest.
How do service workers contribute to making a web application work offline?
- By caching web application resources for offline use.
- By disabling network access entirely.
- By encrypting user data for offline access.
- By optimizing server response times.
Service workers contribute to making a web application work offline by caching web application resources for offline use. Service workers act as a proxy between the web application and the network, intercepting and caching requests. When the user goes offline, the service worker can serve cached content, allowing the web app to continue functioning and providing a seamless offline experience.
When might you use a Fragment in React?
- When you need to group multiple elements without adding extra nodes to the DOM.
- When you want to add event handlers to child elements.
- When you want to apply styling to a group of elements.
- When you want to pass data between parent and child components.
You might use a Fragment in React when you need to group multiple elements without adding extra nodes to the DOM. Fragments are a lightweight way to wrap multiple elements without introducing an additional div or any other node in the DOM. This is useful for maintaining a clean and efficient DOM structure.
You have a React component that uses a third-party library for date manipulation. While testing, you notice that this library is causing issues. How can you isolate your tests from this external dependency using Jest?
- Use Jest's jest.mock to mock the third-party library and control its behavior during testing.
- Rewrite the third-party library's code to remove the issues it's causing.
- Ignore the issues and proceed with testing, assuming they won't affect the test results.
- Disable the use of third-party libraries in the test environment.
To isolate your tests from an external dependency causing issues, you should use Jest's jest.mock as described in option a. This allows you to mock the third-party library's behavior and control its responses during testing. Rewriting the library's code is impractical and not the responsibility of the test suite. Ignoring issues or disabling third-party libraries entirely are not recommended testing practices and may lead to unreliable tests.
The ability of Immutable.js to use previous data structures to efficiently create new ones without deep cloning is referred to as ________.
- Immutable Transformation
- Persistent Data Manipulation
- Structural Optimization
- Structural Sharing
The ability of Immutable.js to use previous data structures to efficiently create new ones without deep cloning is referred to as "Structural Sharing." This core concept of Immutable.js helps optimize memory usage and performance by reusing parts of the existing data structures when creating new ones. Instead of copying everything, it shares common elements, which is key to Immutable.js's efficiency and immutability.
Which of the following is NOT a core principle of Redux?
- Asynchronous actions.
- Changes made through pure functions.
- Immutable state.
- Single source of truth.
Redux follows several core principles, including immutable state, a single source of truth, and changes made through pure functions (reducers). Asynchronous actions, while commonly used with Redux, are not a core principle of Redux itself. They are more of a common practice when handling asynchronous operations in Redux applications.
What is a common naming convention for HOCs in the React community?
- Starting with "ReactHOC_"
- Using PascalCase for component names.
- Prefixing with "with" followed by the component name.
- Starting with "hoc_"
In the React community, a common naming convention for Higher Order Components (HOCs) is to prefix them with "with" followed by the component name they enhance. This convention helps developers identify HOCs and understand their purpose in enhancing components. The other naming conventions mentioned in options 1, 2, and 4 are not as commonly used in the React community for HOCs.
You're optimizing a React application and notice that a particular component re-renders frequently, even though its props and state seem unchanged. Which tool or method can help you verify and prevent this behavior?
- Applying shouldComponentUpdate lifecycle method to the component.
- Enabling PureComponent for the component.
- Profiling with React DevTools.
- Using React.memo for the component.
In this scenario, you can utilize React.memo to optimize the component's re-renders. React.memo is a higher-order component (HOC) that memoizes a component, preventing it from re-rendering when its props remain unchanged. React DevTools can help you identify the problem, but React.memo is the method to prevent unnecessary re-renders.
The TypeScript keyword used to create a type that can be one of several types is called ________.
- union
- any
- object
- function
The TypeScript keyword used to create a type that can be one of several types is called union. Unions are used to specify that a value can have one of several possible types. This is valuable for scenarios where a variable or property can accept multiple data types. The other options (any, object, function) do not specifically define a type that can be one of several types.
You're refactoring a higher-order component that injects props into wrapped components. You notice that the component tree is getting deeper and more complex. Which pattern can help flatten the component tree while still sharing the logic?
- Adapter Pattern
- Composite Pattern
- Facade Pattern
- Proxy Pattern
The Proxy Pattern can help flatten the component tree while still sharing the logic. It allows you to control access to an object by creating a surrogate or placeholder for it. In the context of React or similar frameworks, a proxy component can be used to encapsulate complex logic, making the component tree shallower and more maintainable. The other patterns listed do not directly address this issue.