Week 1

Question 1

What does console.log(…) do in the Node.js environment?

Answer 1

Prints the given argument to the standard output, or terminal
It outputs to the stream known as STDOUT

Question 2

What is the difference to fork and clone a code repository?

Answer 2

Fork copies the repository on the server, and clone copies it to the local disk

Fork is an action used on GitHub to copy a repo to your account

Question 3

What will be logged to the console?
var globalScope = ‘I'm all up in your codes!’;

if (true) {
let globalScope = ‘Not anymore, you're not!’;
}
console.log(globalScope);

Answer 3

I’m all up in your codes!

The let declaration is scoped to it’s containing block, which means that our console.log() ignores it completely.

Question 4

What will be logged to the console?
x = 12;
if(true) {
x + 2;
x = 4;
}
console.log(x);

Answer 4

4

x is set as a global variable, and is not contained inside any function or block scope. It is overwritten inside the conditional statement, and retains it’s new value when the block closes.

Question 5

What will the following code output to the console?

Answer 5

undefined
E.T.
friend is hoisted to the top but given no value, therefore the first console.log will say undefined. Then, the value “E.T.” is set to friend before the second console.log which will output “E.T.”.

Question 6

The functions createUser, or sendUserData are examples of which naming convention?

Answer 6

Camel Case

Question 7

What is meant by type coercion?

Answer 7

When the operands of an operator are different types, one of them will be converted to an equivalent value of the other operand’s type

an example is the comparison operator == in JavaScript

Question 8

What is meant by type coercion?

Answer 8

When the operands of an operator are different types, one of them will be converted to an equivalent value of the other operand’s type

an example is the comparison operator == in JavaScript

Question 9

What would the following JavaScript code evaluate to? Why?

‘0’ == false

Answer 9

true

‘0’ and false would be coerced to a common type and evaluate to be equal (or true)

Question 10

Would the following JavaScript code evaluate to true or false? Why?

‘1’ === 1

Answer 10

false because the variable types are different

Question 11

Which of the following is not a primitive data type in JavaScript? Boolean, Array, Number, String?

Answer 11

arrays are a type of Object in JavaScript, not a primitive

Question 12

Name a valid way to access an object value?

Answer 12

myObject[‘key’]
you can access object values using square bracket notation

myObject.key
you can access values using .key notation

Question 13

Are primitive data types the same across most programming languages?

Answer 13

No, primitives are a defining feature of a programming language

Primitives are similar, but often unique to a given programming language

Question 14

Is the following code a valid Object in JavaScript?

var myObjected = {
‘key-1’: 42,
keyB: ‘value B’,
‘keyC’: [1, 2, 3]
};

Answer 14

Correct, the object would work despite inconsistent key definitions

Question 15

Given the following object, how would you access the first borough, Manhattan (using JavaScript)?
var nyc = {
name: ‘New York City’,
boroughs: [
‘Manhattan’,
‘Queens’,
‘Brooklyn’,
‘The Bronx’,
‘Staten Island’],
population: 8491079,
area_codes: [212, 347, 646, 718, 917, 929],
position: { lat: 40.7127, lng: -74.0059 }
}

Answer 15

nyc[‘boroughs’][0]

This would return the first element of the boroughs array

Question 16

In programming, what is meant by the term First-class citizen (or First-class object)?

Answer 16

An object with no restrictions on its creation, destruction, or usage

This includes the ability to be passed as an argument, returned from a function, and assigned to a variable

Question 17

Can functions act as objects in JavaScript?

Answer 17

Correct, functions are instances of the Object type in JavaScript and can have properties and methods just like any other object

Question 18

Considering the following JavaScript code, is it possible to assign attributes to a function?

const funObject = function() {
console.log(‘I am function.’);
}
funObject.someAttribute = 42;

Answer 18

It is possible because JavaScript functions are also Objects

Functions can be assigned attributes like any other object

Question 19

Which of the following is the best definition of a Higher-order function?

Answer 19

A function that takes a function as an argument, or returns a function as a result
Higher-order functions make use of other functions either as arguments or by returning them

Question 20

What is the rationale behind using Higher-order functions?

Answer 20

They allow for creation of more powerful and generalized functions

A Higher-order function’s job is reduced in scope when you allow it to interact with other functions

Question 21

define an anonymous function

Answer 21

A nameless function defined inline or assigned to a variable. It may or may not be used as a callback function

Anonymous functions can be assigned to variables or simply passed in to another function directly (inline)

Question 22

Given the following JavaScript code, what will be the resulting value of url?

let PORT = 8080;
let url = http://localhost:${PORT}/path;

Answer 22

http://localhost:8080/path

the port will be interpolated into the template literal

Question 23

Considering the following JavaScript code, what will the console output be and why?

const foo = function() {
var x = 1;
if (x === 1) {
let y = 2;
}
console.log(‘Value of y is ‘ + y);
}
foo();

Answer 23

ReferenceError

the block-scoping of let y = 2 makes it available only within the if statement block

Question 24

Consider the following JavaScript code, what would be the console output?

const names = [‘Graham’];
names = [];
console.log(names)

Answer 24

Console would show a TypeError

Assignment to constant variable is not possible due to the declaration using const

Question 25

Given the following JavaScript code, what would be the console output?
const names = [];
names.push(‘Jordan’);
console.log( names );

Answer 25

Console would show [‘Jordan’]

it still allows us to change the value of the referenced variable

Question 26

How are Arrow Functions () => {} different than traditional function expressions?

Answer 26

Arrow Functions do not declare their own scope
arrow functions inherit parent scope

Question 27

What are recursive functions?

Answer 27

A recursive function can stop calling itself if it doesn’t have a base case.

Every recursive function must stop calling itself at some point using a base case, otherwise it will just continue to call itself forever, like an infinite loop.

Question 28

Take a look at the following recursive function:

function countEvenToTwelve(number) {
if (number <= 12) {
console.log(number);
countEvenToTwelve(number+2);
}
}
what is the recursive case?

Answer 28

number <= 12 is the recursive case.

When this is true, the function will call itself again.

Question 29

What purpose does the require() method serve in JavaScript?

Answer 29

It imports functionality (or data) from another module

it allows us to import functions, variables, and objects that are exported by other modules

Question 30

To which directory does NPM install dependencies?

Answer 30

./node_modules

Correct, each dependency has its own subdirectory in the node_modules directory

Question 31

What are the differences between packages, modules, and libraries?

Answer 31

Library: an independent collection of code that can be used by programs (not JS specific) - Module: JS code in a separate file, that can be required by other JS programs - Package: a collection of JS modules, with a package.json, usually published on NPM

Question 32

Should the node_modules directory be committed to your project’s git repo?

Answer 32

no

Question 33

Should the package.json file be committed to a project’s git repo?

Answer 33

yes

Question 34

How can you empty an array in JavaScript?

Answer 34

There are actually a few methods to do this. Lets say you have the following array let array = [1, 2, 3, 4], you can empty it by:

// creates a brand new empty array
array = [];

// clears the array without creating a copy
array.length = 0;

// modifies the array and returns the removed entries
array.splice(0, array.length);

Question 35

Explain the difference between == and ===?

Answer 35

In JavaScript, there are two sets of equality operators. The triple-equal operator === behaves like any traditional equality operator would: evaluates to true if the two expressions on either of its sides have the same type and the same value. The double-equal operator, however, tries to coerce the values before comparing them. It is therefore generally good practice to use the === rather than ==. The same holds true for !== vs !=.

Question 36

What are the six JavaScript data types?

Answer 36

Boolean
Number
String
Null
Undefined
Symbol

Question 37

What would be the result of 3+2+”7”?

Answer 37

Since 3 and 2 are integers, they will be added numerically. And since 7 is a string, it will resort to string concatenation, resulting in a string type. The result would be “57”.

Question 38

Explain JavaScript’s for..in loop.

Answer 38

The for-in loop is used to loop through the properties of an object. More specifically, it loops through each key.

The syntax for the for-in loop is:

for (let key in object) {
// statement or block to execute for each key
}
In each repetition, one property from the object is associated to the variable (named key above), and the loop is continued until all of the properties of the object are depleted.

Question 39

In this example, what does this evaluate to when we run thing.daadaa()?

const thing = {
doodoo: “Boo”,
daadaa: function() {
console.log(this);
}
};

Answer 39

The thing object

When you use this inside a method, this refers to the object that the method was called on.

Question 40

const dog = {
sound: “woof”,
speak: function() {
console.log(this.sound);
}
};

dog.sound = “🐶”
dog.speak();

Answer 40

🐶

The sound property is what is being logged to the console. sound also gets changed to 🐶 before being logged out.