Question 1

What’s the purpose of `async` and `await`?

Accepted Answer

`async` makes a function return a promise, and `await` pauses until it resolves, making async code look sync. It’s way easier to read than `.then()` chains. I use it for fetching data or any async task.

Question 2

How do you format a number as currency?

Accepted Answer

Use `Intl.NumberFormat` to format numbers as currency with locale options—it’s built-in and flexible. You specify the currency and style. I use it for polished UI outputs.

Question 3

How do you implement a factorial function?

Accepted Answer

A factorial function multiplies a number by all positive integers below it—like `5! = 5 * 4 * 3 * 2 * 1`. You can use recursion or a loop; I prefer recursion for clarity, memoizing if performance matters.

Question 4

What is a pure function?

Accepted Answer

A pure function always returns the same output for the same input and has no side effects—like modifying external state. It’s predictable and easy to test. I use them to keep code reliable and maintainable.

Question 5

What is the `Map` object used for?

Accepted Answer

A `Map` holds key-value pairs where keys can be any type (unlike objects, which use strings/symbols). It preserves insertion order and is great for unique mappings. I use it when keys aren’t simple strings.

Question 6

What are JavaScript symbols?

Accepted Answer

Symbols are unique, immutable primitives created with `Symbol()`, often used as object keys to avoid name clashes. They’re hidden from most iteration, making them great for private properties. I use them for special identifiers.

Question 7

How do you create a module in JavaScript?

Accepted Answer

With ES6, you use `export` to define a module and `import` to use it. It keeps code organized and reusable. I prefer modules over old-school IIFEs for cleaner dependency management.

Question 8

What is a closure and how is it useful?

Accepted Answer

A closure lets a function access variables from its outer scope even after that scope has closed. It’s like a memory that sticks around. I use it for private variables or counters—it’s a neat way to keep state without globals.

Question 9

What is a closure’s use case in event handlers?

Accepted Answer

Closures in event handlers keep variables accessible after setup, like counters in clicks. They tie state to the handler without globals. I use them for dynamic, self-contained logic.

Question 10

What is event bubbling?

Accepted Answer

Event bubbling is when an event on an element triggers and then ‘bubbles up’ to its ancestors. It’s how delegation works—events propagate unless stopped. I use it to catch events efficiently.

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