Question 1

How do I refactor JavaScript callbacks to async/await?

Accepted Answer

Wrap callback-based operations in Promises, then consume them with async/await inside try/catch blocks for error handling. Use Promise.all to run independent operations in parallel instead of awaiting them sequentially.

Question 2

How to update JavaScript objects without mutating them?

Accepted Answer

Use the spread operator to create copies with updated properties, such as { ...user, age: 31 }. For arrays, use map, filter, and spread instead of push or splice to keep operations immutable.

Question 3

What is the difference between Promise.all and Promise.allSettled?

Accepted Answer

Promise.all rejects immediately when any promise fails, while Promise.allSettled waits for all promises and reports each result's status as fulfilled or rejected. Use allSettled when partial results are acceptable.

Question 4

Does optional chaining work with nullish coalescing?

Accepted Answer

Yes, they combine well: user?.address?.city ?? 'unknown' safely accesses nested properties and provides a default only for null or undefined. Unlike logical OR, nullish coalescing preserves falsy values like 0 and empty strings.

Question 5

When should I avoid arrow functions in JavaScript?

Accepted Answer

Avoid arrow functions when you need dynamic this binding, such as object methods that reference the instance, event handlers needing the element context, or prototype methods. Arrow functions capture lexical this from the enclosing scope.

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