Q391. What is the purpose of `getSnapshotBeforeUpdate()` lifecycle method?
The new `getSnapshotBeforeUpdate()` lifecycle method is called right before DOM updates. The return value from this method will be passed as the third parameter to `compo...
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Q392. What is the recommended way for naming components?
It is recommended to name the component by reference instead of using `displayName`. Using `displayName` for naming component: ```javascript export default React.createCl...
Q393. What is the recommended ordering of methods in component class?
_Recommended_ ordering of methods from _mounting_ to _render stage_: 1. `static` methods 2. `constructor()` 3. `getChildContext()` 4. `componentWillMount()` 5. `component...
Q394. 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...
Q395. 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...
Q396. 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...
Q397. 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 ...
Q398. What is the difference between `super()` and `super(props)` in React using ES6 classes?
When you want to access `this.props` in `constructor()` then you should pass props to `super()` method. **Using `super(props)`:** ```javascript class MyComponent extends ...
Q399. 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 `...
Q400. 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 ...