ES6

Question 1

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

Answer 1

a self contained piece of code denoted by curly braces {} if else, for, while

Question 2

What does block scope mean?

Answer 2

variables and functions are only accessible inside the block {}

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

The variables declared by the let keyword are mutable
variables created by the const keyword are “immutable” and can’t be reassigned

Question 5

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

Answer 5

adding to an array or object you’re not re-assigning or re-declaring the constant, it’s already declared and assigned, you’re just adding to the “list” that the constant points to.
constant is actually storing a reference to the array. When you join something into your array you are not modifying your constant value, but the array it points to.

constants makes references to the variable but not the actual value of the array.

Question 6

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

Answer 6

If you don’t need to reassign the variable, use const. Otherwise use let

Question 7

What is the syntax for writing a template literal?

Answer 7

Let variableName = String text here with ${variablename}

Question 8

What is “string interpolation”?

Answer 8

String formatting: the ability to substitute part of the string for the values of variables or expressions.

Question 9

What is destructuring, conceptually?

Answer 9

Setting a value of an element to a new variable
taking specific fields out of an object and assigning it to a variable

Question 10

What is the syntax for Object destructuring?

Answer 10

let { property: newVariable, property2: newVariableTwo } = objectName; or can use property as the variable name
for default value, use = defaultvalue

Question 11

What is the syntax for Array destructuring?

Answer 11

Let [newVariable, newVariable2, newVariable3] = arrayName;
if you don’t want some of the items, use commas nothingin between

Question 12

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

Answer 12

Destructuring has the elements on the left and object/array on the right of the =
Object array literals have the elements after the = and the object/array literal name before the =

left hand side, being assigned
right hand side being evaluated

Question 13

What is the syntax for defining an arrow function?

Answer 13

(arguments) => code block, can also use { code block }

Question 14

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

Answer 14

If you use an expression in the body of an arrow function, you don’t need to use the curly braces.
However, if you use a statement, you must wrap it inside a pair of curly braces as in the following example:
single expression is returned from the arrow function

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 instead of creating its own this context.
determined by state of the code, lexical scope
Goes upwards to find the nearest object definition or function

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

Question 18

How do you handle the rejection of a Promise?

Answer 18

Promise.catch

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

Question 20

What is the typeof an ES6 class?

Answer 20

object

Question 21

Describe ES6 class syntax.

Answer 21

Class keyword followed by the name of the class in upper-case followd by a constructor with its associated properties and any possible associated methods within

Class student {
constructor(parameters, here) {
This.property = property;
this.elapsedSeconds = startTimeInSeconds
}
};

Question 22

What is “refactoring”?

Answer 22

process of restructuring existing computer code—changing the factoring—without changing its external behavior

Question 23

How are ES Modules different from CommonJS modules?

Answer 23

Uses import and export instead of require() and module.exports

Question 24

What kind of modules can Webpack support?

Answer 24

ECMAScript modules. CommonJS modules. AMD modules.