How does "styled-components" library in React allow for dynamic styling?
- It generates random styles for each component.
- It imports external CSS files.
- It relies on inline HTML styling.
- It uses a JavaScript object to define styles.
"styled-components" in React allows for dynamic styling by using a JavaScript object to define styles. This approach allows you to use JavaScript logic, including the use of props, to conditionally apply styles to components. Unlike traditional CSS, which is static, styled-components provides a more dynamic way to manage styles in your React application.
How does Immer produce a new state without deep cloning all objects in the state tree?
- It creates a completely new state tree from scratch.
- It relies on JavaScript's native deep cloning functions.
- It uses a third-party library for cloning.
- It utilizes structural sharing to create a new state.
Immer employs structural sharing, also known as "copy-on-write," to generate a new state without deep cloning all objects. When changes are made, only the affected objects are cloned, reducing memory and CPU usage. This technique is crucial for efficient state management in applications, particularly in React and Redux.
Why would you use shouldComponentUpdate in a class component?
- To create custom hooks for functional components.
- To improve code readability in class components.
- To optimize performance by controlling re-renders.
- To specify the initial state of a class component.
shouldComponentUpdate is used in class components to optimize performance by controlling when a component should re-render. By implementing this method, you can define custom logic to determine whether a re-render is necessary based on changes in the component's props or state. It's not related to creating custom hooks, improving code readability, or specifying initial state in class components.
Profiling in React DevTools can help identify components that waste render cycles due to frequent ________ without actual DOM changes.
- Component unmounts
- Redux actions
- Render method calls
- State and props updates
Profiling in React DevTools can help identify components that waste render cycles due to frequent state and props updates without actual DOM changes. This is essential for improving performance, as excessive re-rendering can lead to performance bottlenecks.
In Immutable.js, the method to retrieve a value by its key in a Map is ________.
- access()
- find()
- get()
- retrieve()
In Immutable.js, the method used to retrieve a value by its key in a Map is get(). Immutable.js provides the get() method for accessing values in a Map. It's important to use get() to maintain the immutability of the data structure.
When using the map function to render a list in JSX, it's important to provide a unique ________ to each item.
- Class
- Element
- Index
- Key
When rendering lists in JSX using the map function, it's crucial to provide a unique "key" to each item. This "key" is used by React to efficiently update and re-render elements in the list when needed. Using a unique key helps React identify which elements have changed, been added, or been removed, optimizing performance and preventing rendering issues.
You're building an application where certain operations should only be performed when specific observable properties change. How would you set up a reaction that specifically listens to these properties in MobX?
- When
- autorun()
- computed()
- reaction()
To set up a reaction that specifically listens to certain observable properties in MobX, you would use the reaction() function. The reaction() function allows you to define custom reactions that depend on specific observables. When the specified observables change, the reaction is triggered, allowing you to perform the desired operations. This approach is suitable when you need fine-grained control over reactions.
In JSX, the HTML attribute class is replaced with ________.
- class
- className
- classTag
- cssClass
In JSX, the HTML attribute class is replaced with className. This is because class is a reserved keyword in JavaScript, and JSX is a JavaScript extension. To apply CSS classes to JSX elements, you should use className instead of class.
You're working on an e-commerce website, and the product details page has a 3D product viewer. Given the viewer's heavy resources, what approach would you take to ensure the page loads quickly?
- Increase server capacity to handle the heavy resources.
- Minimize the use of client-side rendering for the 3D viewer.
- Use lazy loading to load the 3D viewer component only when it's in the viewport.
- Use synchronous loading to ensure all components load simultaneously.
To ensure the product details page loads quickly, you should use lazy loading. This technique loads the 3D viewer component only when it's in the viewport, reducing initial page load time. Minimizing client-side rendering and increasing server capacity may help with performance but do not directly address the issue of quick page load for this specific component. Synchronous loading can actually slow down the page.
What is the purpose of the preventDefault method in event handling?
- It defers an event until later execution.
- It halts the execution of the event handler function.
- It prevents an event from being logged to the console.
- It stops the default behavior associated with an event.
The purpose of the preventDefault method in event handling is to stop the default behavior associated with an event. For example, when handling a click event on an anchor tag, preventDefault prevents the browser from navigating to the URL specified in the "href" attribute. It allows you to control and customize how events are handled, preventing their default actions when necessary.