ES6 Cool Features

Question 1

What is used when you don’t want to reassign the variable?

Answer 1

Const

Question 2

What is used when we want to reassign a variable

Answer 2

Let

Question 3

What is an old way to declare variable in javaScript and it’s now the weakest keyword to define a variable

Answer 3

Var

Question 4

What are the differences between Var, Let and Const

Answer 4

1. The main difference is in the visibility or accessibility in some areas of code, ie. scope
2. When you declare a variable in a function it is visible only within that function, you can’t access it outside.
3. Var variables have function scope, while let and const have block scope.
4. With let we avoid overwriting variables in the outer scope
5. Another potential issue with var is that it can be referenced before it’s assigned

Question 5

What allows us to initialize functions with default values?

Answer 5

Default parameters

(These values are used when an argument is either omitted or undefined)

Question 6

What as the name suggests can be included by using the three dots syntax and must be declared at the end of the parameters list?

Answer 6

Rest Parameter

Question 7

What is usually used because of it’s shorter syntax, compared to traditional functions.

Answer 7

Arrow Functions

Question 8

What is one of the benefit of using a normal function over an arrow function when using the this keyword?

Answer 8

1. When we use a normal function as an object method in the function’s body we can use the this keyword to refer to the object itself.

Question 9

What has a concise syntax and makes it ideal to use with array processing and accept callback functions, such as sort( ), map( ), and reduce( ) which changes seemingly complex processes into simpler code?

Answer 9

Arrow functions

Question 10

In ES6 what operator permits the extraction of values from either objects or arrays into distinct variables?

Answer 10

Destructuring

Question 11

What is denoted by three dots “…” and can be used to “unpack” elements of objects, arrays and strings?

Answer 11

Spread Operator

Question 12

When the spread operator is applied on objects, it is usually used to combine objects by…

Answer 12

copying the properties of an existing object into another one

Question 13

What happens when the Spread operator is applied to a string?

Answer 13

It spreads out each individual character of the string into individual characters

Question 14

When applied on arrays, what can also be used to copy all the elements from an array into another, spreading them out in a specified position?

Answer 14

Spread opearator

Question 15

Can a Spread operator be used to concatenate two arrays?

Answer 15

Yes

Question 16

array.some( )

Answer 16

array.some( )

It will return true if at least one element matches the condition specified in the callback, returns false otherwise

Question 17

array.every( )

Answer 17

array.every( )

will return true, if each element matches the condition specified in the callback, otherwise will return false

Question 18

array.flat( )

Answer 18

array.flat( )

(returns a new array)

with all the elements of the subarrays concatenated one specified depth

Question 19

array.find( )

Answer 19

array.find( )

this method finds an element which matches the specified criteria, it returns that element. It stops searching if it finds the element

Question 20

array.findIndex( )

Answer 20

array.findIndex( )

same as .find( ) but it returns the index at which the value is found

Question 21

array.fill( )

Answer 21

array.fill( )

overwrites all the elements in an array with the specified value

Question 22

array.includes( )

Answer 22

array.includes( )

will return true, if the array contains a certain element, and false if not

Question 23

array.slice( )

Answer 23

array.slice( )

(returns a new array)

containg the selected elements only. You can select elements by specifying a start index, and optionally an end index