Q131. What is the purpose of `getDerivedStateFromProps()` lifecycle method?
The new static `getDerivedStateFromProps()` lifecycle method is invoked after a component is instantiated as well as before it is re-rendered. It can return an object to ...
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Tag: state ×
Q132. Why we need to pass a function to setState()?
The reason behind for this is that `setState()` is an asynchronous operation. React batches state changes for performance reasons, so the state may not change immediately...
Q133. Why is `isMounted()` an anti-pattern and what is the proper solution?
The primary use case for `isMounted()` is to avoid calling `setState()` after a component has been unmounted, because it will emit a warning. ```javascript if (this.isMou...
Q134. What is the difference between constructor and getInitialState?
You should initialize state in the constructor when using ES6 classes, and `getInitialState()` method when using `React.createClass()`. **Using ES6 classes:** ```javascri...
Q135. Can you force a component to re-render without calling setState?
By default, when your component's state or props change, your component will re-render. If your `render()` method depends on some other data, you can tell React that the ...
Q136. What is the difference between `setState()` and `replaceState()` methods?
When you use `setState()` the current and previous states are merged. `replaceState()` throws out the current state, and replaces it with only what you provide. Usually `...
Q137. How to listen to state changes?
The `componentDidUpdate` lifecycle method will be called when state changes. You can compare provided state and props values with current state and props to determine if ...
Q138. What is the recommended approach of removing an array element in React state?
The better approach is to use `Array.prototype.filter()` method. For example, let's create a `removeItem()` method for updating the state. ```javascript removeItem(index)...
Q139. What are the possible ways of updating objects in state?
1. **Calling `setState()` with an object to merge with state:** - Using `Object.assign()` to create a copy of the object: ```javascript const user = Object.assign({}, thi...
Q140. How to update a component every second?
You need to use `setInterval()` to trigger the change, but you also need to clear the timer when the component unmounts to prevent errors and memory leaks. ```javascript ...