ES6 Basics

1/25 What value will this expression return?
```
let x, { x: y = 1 } = { x };   y;
```
- { x: 1 }
- 1
- { x : 1 }
- "undefined"
2/25 What will the result of this expression be?
```
typeof (new (class F extends (String, Array) { })).substring
```
- Error
- "undefined"
- "object"
- "function"

3/25 What will this function return?

(function() { 

if (false) {

 let f = { g() => 1 };

 }

 return typeof f;

 })()

Undefined
"object"
"function"
Error

4/25 What result will this expression have?
```
typeof (function* f() { yield f })().next().next()
```
- "generator"
- "object"
- "function"
- Error
5/25 Why is super used?
- Is used for creating and initializing an object.
- It's a simple function.
- Is used as an "object" which calls the parent class.
- Is used as a "function" which calls the parent's constructor.
6/25 ES6 introduces a special "const" declaration. Do you know what it does?
```
const PI = 3.14; 

console.log(PI) //Prints 3.14
```
- It is exactly the same as let.
- It is used to define math-related variables.
- Const turns variables into constants, and they can't be changed.
7/25 ES6 gives you a number of new methods for operating with Strings. Which one replaces this annoying piece of code?
```
let some_text = "some string"; 

if(some_text.indexOf('str') !=-1){

 return true;

 }
```
- some_text.repeat('str');
- some_text.endsWith('str');
- some_text.includes('str');
8/25 Array.from() is a powerful method which converts array-like objects into real Arrays. Why do you use it in the code below?
```
let titleElements = document.querySelectorAll('.article .title') let titles = Array.from(titleElements).map( t => t.textContent ); console.log(titles);
```
- This code is wrong and won't work.
- You use it because it is hip.
- You need it, because querySelectorAll returns a NodeList, which doesn't have the map method, and only arrays do.
9/25 What is the main purpose of the spread operator in ES6?
- To spread objects into arrays
- To expand iterable objects into individual elements
- To combine multiple functions into one
- To spread arrays into objects
10/25 Which statement about arrow functions in ES6 is true?
- They do not have their own 'this' context
- They can be used as constructors
- They are not hoisted
- They have their own 'arguments' object
11/25 In ES6, which keyword is used to import modules?
- require
- import
- include
- load
12/25 What does the 'Set' object introduced in ES6 represent?
- A collection of unique values
- A key-value map
- A sequential list of elements
- A set of functions
13/25 Which of the following is a template literal in ES6?
- 'Hello World'
- `Hello ${name}`
- "Hello " + name
- Hello + name
14/25 What is the output of the following code snippet? `const [a, , b] = [1, 2, 3]; console.log(a, b);`
```
const [a, , b] = [1, 2, 3]; 

console.log(a, b);
```
- 1, 2
- 2, 3
- 1, 3
- undefined, undefined
15/25 In ES6, which syntax is used for defining a class?
- function MyClass() {}
- class MyClass {}
- MyClass = new Class()
- object MyClass {}
16/25 How does 'const' behave differently from 'var' in ES6?
- const variables can be reassigned
- const creates block-level scope
- const does not allow hoisting
- const is not compatible with older browsers
17/25 What is the main advantage of using 'let' over 'var' in ES6?
- let provides function scope
- let supports redeclaration in the same scope
- let provides block-level scope
- let improves performance
18/25 Which new data structure introduced in ES6 stores unique values of any type?
- Array
- Object
- Map
- Set
19/25 How does the 'for...of' loop in ES6 differ from 'for...in'?
- for...of iterates over properties
- for...of is used for objects
- for...of iterates over iterable objects like arrays
- There is no difference
20/25 In ES6, what is the main use of a 'Symbol'?
- To create unique, immutable identifiers
- To symbolize constants
- To enhance security
- To replace strings
21/25 What does the 'Map' object introduced in ES6 represent?
- A collection of key-value pairs
- A list of unique values
- A new way to create arrays
- A mapping function for arrays
22/25 How does 'yield' work in ES6?
- It pauses and resumes a generator function
- It yields control to another function
- It produces a value from a sequence
- It generates random values
23/25 Which of the following is a new string method introduced in ES6?
- .contains()
- .includes()
- .findString()
- .hasText()
24/25 In ES6, what does 'Object.is()' do?
- Checks if two values are the same value
- Checks if an object has a specific property
- Creates a new object
- Compares two objects deeply
25/25 How does the 'endsWith()' method work with ES6 strings?
- It checks if a string ends with a specified substring
- It appends a specified substring to the end of a string
- It removes the specified substring from the end of a string
- It capitalizes the final character of a string
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ES6 Basics

1/25 What value will this expression return?

2/25 What will the result of this expression be?

3/25 What will this function return?

4/25 What result will this expression have?

5/25 Why is super used?

6/25 ES6 introduces a special "const" declaration. Do you know what it does?

7/25 ES6 gives you a number of new methods for operating with Strings. Which one replaces this annoying piece of code?

8/25 Array.from() is a powerful method which converts array-like objects into real Arrays. Why do you use it in the code below?

9/25 What is the main purpose of the spread operator in ES6?

10/25 Which statement about arrow functions in ES6 is true?

11/25 In ES6, which keyword is used to import modules?

12/25 What does the 'Set' object introduced in ES6 represent?

13/25 Which of the following is a template literal in ES6?

14/25 What is the output of the following code snippet? `const [a, , b] = [1, 2, 3]; console.log(a, b);`

15/25 In ES6, which syntax is used for defining a class?

16/25 How does 'const' behave differently from 'var' in ES6?

17/25 What is the main advantage of using 'let' over 'var' in ES6?

18/25 Which new data structure introduced in ES6 stores unique values of any type?

19/25 How does the 'for...of' loop in ES6 differ from 'for...in'?

20/25 In ES6, what is the main use of a 'Symbol'?

21/25 What does the 'Map' object introduced in ES6 represent?

22/25 How does 'yield' work in ES6?

23/25 Which of the following is a new string method introduced in ES6?

24/25 In ES6, what does 'Object.is()' do?

25/25 How does the 'endsWith()' method work with ES6 strings?