ES6

Question 1

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

Answer 1

1. Portions of code denoted by curly braces {}.
2. Some examples are if/else, for, while, try/catch.

Question 2

What does block scope mean?

Answer 2

Variables declared within that code block can’t be accessed by code outside of the block

Question 3

What is the difference between var and let?

Answer 3

Var adds the variable to the property list of the global object (window for browsers) —> let does not.

Question 4

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

Answer 4

They’re both block scoped.

Question 5

What is the difference between const and let?

Answer 5

1. Block-scoped variables assigned by const keyword can not be reassigned.
2. You also have to initialize a value to the variable declared by const —> you don’t have to immediately with let.

Question 6

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

Answer 6

The array is not immutable, it can change. It’s just the variable that stores the array that can’t be changed.

Question 7

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

Answer 7

Unless you’re positive you’re going to change the memory pointer, use const.

Question 8

What is the syntax for writing a template literal?

Answer 8

Use backticks (string-goes-here)

Question 9

What is string interpolation?

Answer 9

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

Question 10

What is destructuring, conceptually?

Answer 10

Taking an array or object and assigning some OR all values to corresponding variables

Question 11

What is the syntax for Object destructuring?

Answer 11

Let { property1: variable1, property2: variable2 } = object

Question 12

What is the syntax for Arrray destructuring?

Answer 12

[a, b, c] = [value1, value2, value3] OR let [x, y, z] = getScores( )

Question 13

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

Answer 13

The variables are always wrapped in an object / array and the sides are swapped.

Question 14

What is the syntax for defining an arrow function?

Answer 14

Const functionName = (parameters) => {code block w/optional return}

Question 15

If an arrow function only has one parameter, we can…

Answer 15

Remove the parenthesis entirely

Question 16

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

Answer 16

Implicit return—> curly braces need an explicit return

Question 17

What determines the ‘this’ inside of a function created with the function keyword?

Answer 17

It’s determined by what is to the left of the dot when the function is called

This is the window object by default —> for methods its the object attached to that method

Question 18

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

Answer 18

It’s a ‘lexical’ this —> this is determining by the surrounding scope

Question 19

Before ES6, how did we change the binding of this to be the appropriate object instead of the window?

Answer 19

Use the bind method with the ‘this’ passed in as an argument

Question 20

When do we need to be extra cautious about ‘this’?

Answer 20

When using callback functions!

Question 21

What are the two ways to fix the binding of this within callback functions?

Answer 21

1. Use the bind keyword
2. Use arrow functions

Question 22

What are two large differences between defining functions using the function keyword and arrow functions?

Answer 22

1. Function definition also has access to the arguments keyword which allows you to loop through the arguments passed into the function
2. Arrow functions don’t bind the this —> they take the this from the enclosing scope

Question 23

What are the three states a promise can be in?

Answer 23

Pending, fulfilled, rejected

Question 24

How do you handle the fulfillment of a promise?

Answer 24

Use .then(firstArgFx)

Question 25

How do you handle the rejection of a promise?

Answer 25

Use .then(secondArgCbFx) OR .catch

Question 26

How are ES Modules different from CommonJS modules?

Answer 26

CommonJS uses require & module.exports whereas ES modules use import / export.

Question 27

What kind of modules can Webpack support?

Answer 27

It natively supports ES modules, CommonJS modules, and AMD modules

Question 28

The two types of ES6 exports are…

Answer 28

Default exports (can be assigned any name in import file)

Named exports (have to be assigned same name in import file)

Question 29

Why index.js?

Answer 29

We often import things from a lib folder —> create an index.js for that folder and then pull all of the imports from the index.js for that folder