ES6 Basics

1/25 Rest is a new way for functions to handle an arbitrary number of parameters. Can you guess what the mysterious "a" variable holds?
```
function mystery(...params) {
  return params; 
}
let a = mystery(1,23,4);
```
- "a" is undefined
- "a" becomes [1,23,4]
- "a" becomes "1 23 4"
- "a" becomes 1 23 4

2/25 What will this function return?

(function() {
 let f = this ? class g { } : class h { };
 return [ typeof f, typeof h ];
 })();

["undefined", "undefined"]
["function", "function"]
["function", "undefined"]
Error

3/25 What value will this expression return?
```
[...[...'...']].length
```
- 3
- 6
- 9
- Error

4/25 What will this function return?

(function() { 
if (false) {
 let f = { g() => 1 };
 }
 return typeof f;
 })()

Undefined
"object"
"function"
Error

5/25 What result will this expression have?
```
typeof (function* f() { yield f })().next().next()
```
- "generator"
- "object"
- "function"
- Error
6/25 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.
7/25 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.
8/25 What is stored in the triangle array?
```
let point = [1,3], segment = [point,[5,5]], triangle = [...segment,[1,8]];
```
- 23
- [1,3,5,5,1,8]
- [ [1,3], [5,5], [1,8] ]

9/25 Is this a valid code?

class Slave { // ... };
 const slave = Slave();

10/25 Which method introduced in ES6 is used to merge two or more arrays?
- Array.join()
- Array.concat()
- Array.merge()
- Array.combine()
11/25 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
12/25 In ES6, which keyword is used to import modules?
- require
- import
- include
- load
13/25 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
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 Which ES6 feature allows for declaring read-only named constants?
- let
- var
- const
- static
16/25 Which ES6 feature is used to write expressions in a more concise way?
- Arrow Functions
- Template Literals
- Promises
- Destructuring Assignment
17/25 In ES6, which statement correctly imports a single export from a module?
- import { myExport }
- import myExport from 'module'
- require('module').myExport
- load myExport from 'module'
18/25 In ES6, what is the main use of a 'Symbol'?
- To create unique, immutable identifiers
- To symbolize constants
- To enhance security
- To replace strings
19/25 In ES6, which statement correctly creates a class that extends another class?
- class SubClass extends BaseClass {}
- class SubClass inherits BaseClass {}
- SubClass.prototype = new BaseClass();
- class SubClass: BaseClass {}
20/25 Which method in ES6 is used to copy an object?
- Object.copy()
- Object.clone()
- Object.assign()
- Object.duplicate()
21/25 In ES6, what is the purpose of 'WeakSet'?
- To store a weakly held set of unique values
- To create a set with weakened security
- To store a set of weak references
- To create a less efficient version of Set
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 is the result of using a template literal inside another template literal?
- Syntax error
- The inner template literal is ignored
- Nested template processing
- Automatic string conversion
25/25 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
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ES6 Basics

1/25 Rest is a new way for functions to handle an arbitrary number of parameters. Can you guess what the mysterious "a" variable holds?

2/25 What will this function return?

3/25 What value will this expression return?

4/25 What will this function return?

5/25 What result will this expression have?

6/25 Why is super used?

7/25 ES6 introduces a special "const" declaration. Do you know what it does?

8/25 What is stored in the triangle array?

9/25 Is this a valid code?

10/25 Which method introduced in ES6 is used to merge two or more arrays?

11/25 Which statement about arrow functions in ES6 is true?

12/25 In ES6, which keyword is used to import modules?

13/25 What does the 'Set' object introduced in ES6 represent?

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

15/25 Which ES6 feature allows for declaring read-only named constants?

16/25 Which ES6 feature is used to write expressions in a more concise way?

17/25 In ES6, which statement correctly imports a single export from a module?

18/25 In ES6, what is the main use of a 'Symbol'?

19/25 In ES6, which statement correctly creates a class that extends another class?

20/25 Which method in ES6 is used to copy an object?

21/25 In ES6, what is the purpose of 'WeakSet'?

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 is the result of using a template literal inside another template literal?

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