JavaScript ES6+ Features 4

Question 1

What happens when you use `new` with an arrow function?

Accepted Answer

It throws a TypeError because arrow functions cannot be constructors

Answer

Arrow functions lack a `[[Construct]]` internal method, so calling `new` on them throws a `TypeError`.

Question 2

What does `Object.assign({}, obj1, obj2)` do?

Accepted Answer

Merges own enumerable properties of obj1 and obj2 into a new object shallowly

Answer

`Object.assign` copies own enumerable properties from source objects into the target, performing a shallow merge.

Question 3

In ES6 destructuring, what does `const { a: renamed } = obj` accomplish?

Accepted Answer

Extracts obj.a into a variable named 'renamed'

Answer

The `: renamed` syntax in destructuring assigns the value of `obj.a` to a local variable called `renamed`.

Question 4

What is the purpose of `Proxy` in ES6?

Accepted Answer

To intercept and redefine fundamental operations on an object

Answer

A `Proxy` wraps an object and intercepts operations like property access, assignment, and function calls via handler traps.

Question 5

Which of the following is a valid use of computed property names in ES6?

Accepted Answer

const obj = { [key]: value }

Answer

ES6 computed property names use square brackets `[expression]` inside an object literal to use a dynamic expression as the property key.

JavaScript Practice Test