Q651. What is the output of below spread operator array?
```javascript [..."John Resig"]; ``` The output of the array is ['J', 'o', 'h', 'n', ' ', 'R', 'e', 's', 'i', 'g'] **Explanation:** The string is an iterable type and the...
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Q652. What is the difference between HOCs and Hooks?
Both **Higher-Order Components (HOCs)** and **Hooks** let you reuse logic across components, but they solve that problem in very different ways. | Aspect | Higher-Order C...
Q653. Is PostMessage secure?
Yes, postMessages can be considered very secure as long as the programmer/developer is careful about checking the origin and source of an arriving message. But if you try...
Q654. Does `React.memo` prevent Context consumers from re-rendering?
**No.** `React.memo` only performs a shallow comparison of a component's **props** — it has no visibility into context. If a component reads a value via `useContext`/`Con...
Q655. What are the problems with postmessage target origin as wildcard?
The second argument of postMessage method specifies which origin is allowed to receive the message. If you use the wildcard “\*” as an argument then any origin is allowed...
Q656. How would you create a reusable Context?
A **reusable Context** bundles the `createContext` call, its `Provider` (with local state/logic), and a custom hook to consume it into a single module. This hides the raw...
Q657. How do you avoid receiving postMessages from attackers?
Since the listener listens for any message, an attacker can trick the application by sending a message from the attacker’s origin, which gives an impression that the rece...
Q658. Why is Redux Toolkit recommended over Redux?
**Redux Toolkit (RTK)** is the official, opinionated way to write Redux logic today. It's built on top of plain Redux and re-exports its APIs, but wraps them with utiliti...
Q659. Can I avoid using postMessages completely?
You cannot avoid using postMessages completely(or 100%). Even though your application doesn’t use postMessage considering the risks, a lot of third party scripts use post...
Q660. What is the difference between client state and server state?
**Client state** is data that lives entirely in the browser and is owned by the UI — it doesn't need to be synchronized with a backend. **Server state** is data that actu...