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 String interpolation is a much-needed new feature that is finally available in JavaScript. See the example below. Is there anything wrong with it?
```
let name = 'Harry';

let occupation = 'wizard';

console.log(`Hi! My name is ${name}. I'm a ${occupation}.`);
```
- Nothing wrong with the example. This is how the feature works in ES6.
- The example is wrong. You can't break a String into lines in JavaScript.
- The example is wrong. You can't embed variables in String in JavaScript.
- None of the above.
3/25 What value will this expression return?
```
let x, { x: y = 1 } = { x };   y;
```
- { x: 1 }
- 1
- { x : 1 }
- "undefined"
4/25 What value will this expression return?
```
[...[...'...']].length
```
- 3
- 6
- 9
- Error
5/25 What will the result of this expression be?
```
typeof (new (class F extends (String, Array) { })).substring
```
- Error
- "undefined"
- "object"
- "function"
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 ES6 gives an alternative way to assign variables. Can you guess what the below code does?
```
let a = 12, b = 3;

[a, b] = [b, a];
```
- Makes both a and b equal 12.
- Swaps the values inside a and b, without using extra variables.
- Creates an array that contains a and b.
9/25 Which method introduced in ES6 is used to merge two or more arrays?
- Array.join()
- Array.concat()
- Array.merge()
- Array.combine()
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 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
14/25 In ES6, which syntax is used for defining a class?
- function MyClass() {}
- class MyClass {}
- MyClass = new Class()
- object MyClass {}
15/25 What is the result of using '...' in function parameters?
- Spread Operator
- Rest Parameters
- Destructuring
- Array Concatenation
16/25 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'
17/25 What feature in ES6 allows for default parameter values in functions?
- Default Assignment
- Parameter Initialization
- Default Parameters
- Optional Parameters
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 What is the main feature of 'Async/Await' introduced in ES8 (ECMAScript 2017)?
- Synchronous programming
- Error handling
- Asynchronous programming
- Parallel processing
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 String interpolation is a much-needed new feature that is finally available in JavaScript. See the example below. Is there anything wrong with it?

3/25 What value will this expression return?

4/25 What value will this expression return?

5/25 What will the result of this expression be?

6/25 Why is super used?

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

8/25 ES6 gives an alternative way to assign variables. Can you guess what the below code does?

9/25 Which method introduced in ES6 is used to merge two or more arrays?

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

14/25 In ES6, which syntax is used for defining a class?

15/25 What is the result of using '...' in function parameters?

16/25 In ES6, which statement correctly imports a single export from a module?

17/25 What feature in ES6 allows for default parameter values in functions?

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 What is the main feature of 'Async/Await' introduced in ES8 (ECMAScript 2017)?

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