JS ES6

Question 1

What is a code block? What are some examples of a code block?

Answer 1

statements to be excecuted within curly braces; function, loop, conditional

Question 2

What does block scope mean?

Answer 2

exist within curly braces

Question 3

What is the scope of a variable declared with const or let?

Answer 3

block-scope

Question 4

What is the difference between let and const?

Answer 4

variables created with const cannot have values reassigned

Question 5

Why is it possible to .push() a new value into a const variable that points to an Array?

Answer 5

the variable is not being reassigned, the content of the array is being updated

Question 6

How should you decide on which type of declaration to use?

Answer 6

depending on if the variable will need to be reassigned

Question 7

What is the syntax for writing a template literal?

Answer 7

use backticks instead of single/double quotes

Question 8

What is “string interpolation”?

Answer 8

the ability to substitute part of the string for the values of variables or expressions

Question 9

What is destructuring, conceptually?

Answer 9

taking object/array apart by either properties or index and reassigning them to new variables

Question 10

What is the syntax for Object destructuring?

Answer 10

let { property names seperated by commas} = objname

Question 11

What is the syntax for Array destructuring?

Answer 11

let [variable names seperated by commas] =arrayname

Question 12

How can you tell the difference between destructuring and creating Object/Array literals?

Answer 12

destructuring has the assignment operator after the curly braces/square brackets rather than when they are being created the assignment operator is before the curly braces/square brackets

Question 13

What is the syntax for defining an arrow function?

Answer 13

parameters enclosed in parentheses followed by arrow and curly braces; function word is ommited

Question 14

When an arrow function’s body is left without curly braces, what changes in its functionality?

Answer 14

return statement is not needed and only one statement can be executed in the function without curly braces

Question 15

How is the value of this determined within an arrow function?

Answer 15

the value of this is determined at definition

Question 16

What are the three states a Promise can be in?

Answer 16

pending, fulfilled, rejected

Question 17

How do you handle the fulfillment of a Promise?

Answer 17

Promise.then(callback function)

Question 18

How do you handle the rejection of a Promise?

Answer 18

Promise.catch(callback function)

Question 19

What is Array.prototype.filter useful for?

Answer 19

creates a new array with all elements that pass the test implemented by the provided function.

Question 20

What is Array.prototype.map useful for?

Answer 20

creates a new array populated with the results of calling a provided function on every element in the calling array

Question 21

What is Array.prototype.reduce useful for?

Answer 21

executes a reducer function (that you provide) on each element of the array, resulting in single output value.

Question 22

What is “syntactic sugar”?

Answer 22

syntax within a programming language that is designed to make things easier to read or to express

Question 23

What is the typeof an ES6 class?

Answer 23

function

Question 24

Describe ES6 class syntax.

Answer 24

class Name {
    method( ) {
   }
}

Question 25

What is “refactoring”?

Answer 25

process of restructuring existing code without changing its behavior

Question 26

How are ES Modules different from CommonJS modules?

Answer 26

ES6 modules are pre-parsed in order to resolve further imports before code is executed. CommonJS modules load dependencies on demand while executing the code

Question 27

What kind of modules can Webpack support?

Answer 27

ECMAScript modules, CommonJS modules, Asynchronous Module Definition (AMD) modules

Question 28

What must the return value of myFunction be if the following expression is possible? myFunction()();

Answer 28

a function

Question 29

What does this code do?
const wrap = value => () => value;

Answer 29

returns a function that returns a value and assigns it to the const wrap

Question 30

In JavaScript, when is a function’s scope determined; when it is called or when it is defined?

Answer 30

when it’s defined

Question 31

What allows JavaScript functions to “remember” values from their surroundings?

Answer 31

closures