JavaScript ES6+ Features 2

Question 1

What does the `Symbol.iterator` protocol enable in ES6?

Accepted Answer

Making objects iterable with for...of loops

Answer

Implementing `Symbol.iterator` makes any object iterable, allowing it to be used with `for...of` and spread syntax.

Question 2

Which ES6 feature allows a function to pause execution and resume later?

Accepted Answer

Generator functions

Answer

Generator functions, declared with `function*`, use the `yield` keyword to pause execution and resume on the next `.next()` call.

Question 3

What is the output of: `console.log(typeof Symbol('id'))`?

Accepted Answer

'symbol'

Answer

The `typeof` operator returns `'symbol'` for Symbol values, which is a primitive type introduced in ES6.

Question 4

What does `Array.from({length: 3}, (_, i) => i)` return?

Accepted Answer

[0, 1, 2]

Answer

`Array.from` creates an array from an array-like object and applies the mapping function, using the index `i` to produce `[0, 1, 2]`.

Question 5

How do you define a private-like property using WeakMap in ES6?

Accepted Answer

Store the instance as a key and the data as its value in the WeakMap

Answer

Before the `#` private field syntax, WeakMaps with the instance as the key were the idiomatic ES6 pattern for encapsulating private state.

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