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.
Why is binding necessary for event handlers in class components?
- It binds state to the event handler function.
- It ensures that events are handled by the DOM elements.
- It establishes a connection between components.
- It prevents memory leaks in event handling.
Binding is necessary for event handlers in class components to prevent memory leaks. Without binding, the "this" keyword inside the event handler refers to the global context, not the component instance. This can lead to memory leaks as event handlers won't be properly cleaned up. By binding the event handler to the component instance, you ensure that "this" refers to the component, avoiding memory leaks.
In Redux, to handle asynchronous logic, you often use middleware like ________.
- Redux-logger
- Redux-router
- Redux-saga
- Redux-thunk
In Redux, handling asynchronous logic is typically done using middleware like Redux-thunk. Redux-thunk allows you to write action creators that return functions instead of plain objects, enabling asynchronous operations like API calls within Redux. Redux-saga, Redux-logger, and Redux-router serve different purposes and are not used for handling asynchronous logic.
You are building a MobX store for a to-do application. Whenever a task is marked as completed, you want to automatically update the total count of completed tasks. Which MobX feature would be best suited for this?
- Actions
- Computed Property
- Observables
- Reactions
In this scenario, a Computed Property in MobX would be best suited. Computed properties automatically update whenever the observable data they depend on changes. By defining a computed property for the total count of completed tasks, you ensure it updates automatically when the completion status of tasks changes. It's an efficient way to derive data from observables.
In scenarios where performance is critical, how can immutability assist in optimizing React's reconciliation process?
- It adds complexity to the reconciliation process.
- It increases the frequency of deep component rendering.
- It prevents React from performing reconciliation.
- It reduces the need for shallow comparisons during updates.
Immutability can optimize React's reconciliation process by reducing the need for shallow comparisons during updates. Since immutable data structures don't change, React can quickly determine if props or state have changed by comparing references, resulting in faster updates and improved performance, especially in large and complex React applications.
HOCs can introduce potential naming collisions due to the automatic passing of ________.
- Context
- Methods
- Props
- State
Higher-Order Components (HOCs) automatically pass props to the wrapped component. This can introduce potential naming collisions if the same prop name is used within the HOC and the wrapped component. Developers need to be aware of this and avoid naming conflicts when creating or using HOCs.
How does React's diffing algorithm handle the update of lists?
- By comparing the old list to the new list element by element.
- By delegating list updates to the browser's rendering engine.
- By replacing the old list with the new list entirely.
- By using a hashing function to identify changes.
React's diffing algorithm updates lists by comparing the old list to the new list element by element. It identifies changes, additions, and removals, allowing for efficient updates without recreating the entire list. This approach is known as "keyed reconciliation" and helps minimize the DOM manipulation required. This is a crucial concept in optimizing React applications.
To store the previous state or props in functional components, you can use the ________ hook.
- useEffect
- useMemo
- useRef
- useState
To store the previous state or props in functional components, you can use the "useRef" hook. The useRef hook allows you to create mutable references to DOM elements and can be used to store previous values. While the other hooks (useState, useEffect, useMemo) are essential in functional components, they serve different purposes.