es6

Question 1

What is a code block? What are some examples?

Answer 1

a block of code contained by curly braces - loops, if conditions, functions

Question 2

What does block scope mean?

Answer 2

• the block scoped variable is limited in scope to the block in which it was defined. example:

let x = 10;

if (x = 10) {
let x = 20;
console.log(x); // 20: reference x inside the block
}
console.log(x); // 10: reference x at the beginning of the script

Question 3

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

Answer 3

block-scoped

Question 4

What is the difference between let and const?

Answer 4

variables declared by const keyword cannot be reassigned

Question 5

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

Answer 5

The const variable is immutable but the values within the array aren’t immutable

Question 6

How should you decide on which type of declaration to use? (const vs let)

Answer 6

• if the variable will be reassigned, use let

- if the variable is never reassigned, use const

Question 7

What is the syntax for writing template literals?

Answer 7

let example = ` this is a template literal `;

Question 8

What is “string interpolation”?

Answer 8

the ability to substitute part of the string for the values of variables or expressions
- (the big difference between template literals and normal strings is substitution. string interpolation allows you to embed variables and expressions in a string. JS will automatically replace these variables/expressions with their values)

Question 9

what is destructuring, conceptually?

Answer 9

makes it possible to unpack values from arrays, or properties from objects, into distinct variables.

Question 10

What is the syntax for object destructuring?

Answer 10

const {property1: variable1, property2: variable2,,} = objectName

Question 11

What is the syntax for array destructuring?

Answer 11

let [element1, element2, element3,,] = arrayName

Question 12

How can you tell the difference between destructuring and creating object/array literals?

Answer 12

• brackets on the left side of = , destructuring

- if creating object/array, brackets are on the right side of the =

Question 13

What is the syntax for defining an arrow function?

Answer 13

const funcName = (parameter1, parameter2,…) => { code }

Question 14

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

Answer 14

• nothing changes if you use a single expression in the code block.
• if you use a statement or multiple lines of code, braces are needed
  (arrow functions dont magically know what or when to return)

Question 15

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

Answer 15

• an arrow function captures the this value of the enclosing context
• arrow functions establish “this” based on the scope the arrow function is defined within
• determined at definition time instead of call time

Question 16

What are the three states a Promise can be in?

Answer 16

• pending : initial state, neither fulfilled or rejected
• fulfilled : meaning that the operation was completed successfully
• rejected : meaning that the operation failed

Question 17

How do you handle fulfillment of a Promise?

Answer 17

• use the ‘.then’ method

Question 18

How do you handle the rejection of a Promise?

Answer 18

• use the ‘.catch’ method

Question 19

What is “syntactic sugar”?

Answer 19

• syntax within a programming language that is designed to make things easier to read or to express. makes the language “sweeter” for human use

Question 20

Describe ES6 class syntax:

Answer 20

• declare a class followed by a { class body}
• define 0 or more prototype methods of the class

class Name { 
     constructor(param1, param2,..) {

 Prototype method( ) {}

}

Question 21

What is refactoring?

Answer 21

• restructuring existing code without changing its external behavior
• to improve the design, structure, and implementation of the software while preserving its functionality

Question 22

How are ES6 modules different from CommonJS modules?

Answer 22

• ES6 module syntax is part of the language, while CommonJS is a community “bolt-on”
• different syntax (imports/exports instead of require)
• import/exports are static rather than dynamic

Question 23

What kind of modules can Webpack support?

Answer 23

• EcmaScript Modules (ES6)
• CommonJS Modules
• AMD Mdules
• WebAssembly Modules