General

Question 1

What’s it called when you create a conditional to stop a program from breaking?

• checks the passed-in parameters, and returns with an error if they’re not suitable.
• checks the state of the object, and bails out if the function call is inappropriate.
• checks for trivial cases, and gets rid of them quickly.

Answer 1

guard clause

Question 2

What are the advantages and disadvantages of using pseudocode

Answer 2

AD

• Can brainstorm without worrying about syntax

DIS

• can’t check logic
• still too detailed for complex programs.

Question 3

You want to write code without having to worry about syntax, what do you use?

Answer 3

PSEUDOCODE is writing code without worrying about syntax. Casual pseudocode uses plain words to think out the code steps Casual example: Given a collection of numbers. Iterate through the collection one by one. - save the first value as the starting value. - for each iteration, compare the saved value with the current value. - if the current number is greater - reassign the saved value as the current value - otherwise, if the current value smaller or equal - move to the next value in the collection After iterating through the collection, return the saved value.

Formal pseudocode uses specific KEYWORDS to think out the code. Formal example:

START # Given a collection of integers called “numbers”

SET iterator = 1

SET savedNumber = value within numbers collection at space 1

WHILE iterator <= length of numbers

SET currentNumber = value within numbers collection at space “iterator”

IF currentNumber > savedNumber savedNumber = currentNumber

ELSE skip to the next iteration iterator = iterator + 1

PRINT savedNumber

END

Question 4

PesudoCode for:

start of the program

set a variable that we can use for later

retrieve input from user

display output to user

retrieve a value from a variable

show conditional branches in logic

show looping logic

end of the program

Answer 4

START

SET

GET

PRINT

READ

IF/ELSE

IF

ELSE

WHILE

END

Question 5

(Flow chart) Shape of:

Start and Stop

Processing Step

Input/Output

Decision

Connector

Answer 5

https://d1b1wr57ag5rdp.cloudfront.net/images/flowchart_components.jpg

Start and Stop, oval

Processing Step, rectangle

Input/Output, parallelogram

Decision, diamond

Connector, circle

Question 6

Difference between declarative syntax vs imperative syntax?

What’s a metaphor.

When should you use one over the other?

Answer 6

Declarative programming is when you say what you want,

and imperative language is when you say how to get what you want step by step

“I declare that I want this”

“It is imperative that you do each of these things”

Imperative goes to a restaurant and orders a 6oz. steak (cooked rare), fries (with ketchup), a side-salad (with ranch), and a Coke (with no ice). The waiter delivers exactly what he asked for, and he’s charged $14.50. On the other hand,

Declarative goes to a restaurant and tells the waiter that he only wants to pay around 12 dollars for dinner, and he’s in the mood for steak. The waiter returns with a 6oz. steak (cooked medium), a side of mashed potatoes, steamed broccoli, a dinner roll, and a glass of water. He’s charged $11.99.

Declarative is higher level and easier to understand. Use it first. Like pseudocode.

Then use imperative to see how to do it.

Do it top down.

Question 7

Install 3 lint packages locally

(They do not recommend installing globally)

use it to check the code in terminal

Answer 7

npm install eslint eslint-cli babel-eslint –save-dev

npx eslint file_name.js

Question 8

Hotkey to change all variable names

Answer 8

F2

Question 9

What is a template literal?

What are the things it allows called? (1 thing, 2 terms)

Answer 9

Template literals are literals delimited with backticks (`), allowing embedded expressions called substitutions.

With backticks, string literals allowing embedded expressions within:

${ }

Question 10

install readline sync so you can have input in terminal

Answer 10

npm install readline-sync –save

Question 11

What is the difference between a statement and an expression.
{edit with info from this: https://www.youtube.com/watch?v=eWTuFoBYiwg}

Answer 11

Statement vs Expression

Expressions produce a value, and that value will be passed into the function. Statements don’t produce a value, and so they can’t be used as function arguments.

Statement- group of words, numbers and operators that commands an action for the computer to perform

Expression- Any unit of code that can be evaluated to a value is an expression.

console.log((/* Some chunk of JS here */)
Error is a statement. Works is an expression

For example:
a = b * 2;
This statement (is this a statement? It runs in console.log) has four expressions in it:
• 2 is a literal value expression.
• b is a variable expression, which means to retrieve its current value.
• b * 2 is an arithmetic expression, which means to do the multiplication.
• a = b * 2 is an assignment expression, which means to assign the result of the b * 2 expression to the variable a (more on assignments later).

1 statement
console.log(“Hello”);
4 expressions
console
console.log
“Hello”
console.log(“Hello”)

Question 12

What does a block do?

How is it noted/created?

Answer 12

Blocks have two functions:

1. to group statements so that they can be treated as one statement;
2. and to define scopes for names to distinguish them from the same name used elsewhere. In a block-structured programming language, the objects named in outer blocks are visible inside inner blocks, unless they are masked by an object declared with the same name.

a block is defined by wrapping one or more statements inside a curly-brace pair
{ .. }

Question 13

What all will evaluate to false (are falsy) when converted to boolean?
How many things?

Answer 13

null
undefined
NaN
0
false
‘’ (empty string)

Question 14

What is returned from:
2 && 1
0 && 2
2 && 0

3 || 2
2 || 0
0 || 2

Answer 14

1
0
0

3
2
2

Question 15

Return equality with implicit conversion or explicit equality
Return non-equality with implicit conversion or explicit equality

Answer 15

== implicit equality

=== implicit equality

!= implicit non equality
!== implicit equality

Question 16

In what order are method chains processed?

Answer 16

‘string another string’.toUpperCase().toLowerCase()

will return:

string another string

Chains are processed one at a time from left to right.

Question 17

How to actually test truthiness (2 ways)

Answer 17

!!

Boolean()

Question 18

What does a ; indicate?

Answer 18

; indicates the end of a statement

statements can be separated with a ;

Question 19

A new line

implicitly indicates an end of statement (;)

T or F

Answer 19

It depends:

A new line implies a semicolon in most case

console. log(‘affs’)
console. log(‘affs’)

But sometimes it doesn’t:

alert(3 +
1
+ 2);

Sometimes JS assumes right or wrong

Question 20

Enable/modify features added in ECMAScript 5 (ES 5)

what are some of these features?

Answer 20

‘use strict’

Strict mode helps out in a couple ways:

It catches some common coding bloopers, throwing exceptions.

It prevents, or throws errors, when relatively “unsafe” actions are taken (such as gaining access to the global object).

It disables features that are confusing or poorly thought out.

Question 21

Difference between var, let and const

Answer 21

Let has block scope

var has function scope

const has block scope, cannot be reassigned, and must be initialized or will throw an error

Question 22

Most important things when naming a variable:

Answer 22

Use human-readable names like userName or shoppingCart.

Stay away from abbreviations or short names like a, b, c, unless you really know what you’re doing.

Make names maximally descriptive and concise. Examples of bad names are data and value. Such names say nothing. It’s only okay to use them if the context of the code makes it exceptionally obvious which data or value the variable is referencing.

Agree on terms within your team and in your own mind. If a site visitor is called a “user” then we should name related variables currentUser or newUser instead of currentVisitor or newManInTown.

Question 23

For :

const birthday = ‘18.04.1982’;

const age = someCode(birthday);

should birthday and/or age be capitalized?

Answer 23

Just BIRTHDAY because it is hard coded before run time

age has to be calculated still and won’t be known until the function plays.

Question 24

Is null the absence of a value?

Answer 24

No. It is not an undefined value. It is a value DEFINED to be “nothing”, “empty” or “unknown”.

Null is not a “reference to a non-existing object” or a “null pointer” like in some other languages.

Question 25

When should you do this:

let myVariable = undefined

Answer 25

Probably never.

If you want to denote the absence of a value, use null.

Leave undefined as the default initial value for unassigned things.

Question 26

What does:

alert(2+2)

do?

Answer 26

Sends an alert in browser:

4

and waits for user to press “ok”

It changes it into a string after doing math

Question 27

What does alert((function(x) {})) do?

What does console.log((function(x) {})) do?

Answer 27

Send a modal window with it converted to a string (string of function code): function(x) {}

It doesn’t convert it to a string, it just shows the function name: [Function (anonymous)]

Question 28

What is the name of the window that pops up in browser?

Answer 28

a modal (mow-dl) window

Question 29

What do the square brackets denote?

result = prompt(title, [default]);

Answer 29

Optional argument

Question 30

Get user input string in a modal window.

What happens if they press escape?

How do you account for this?

Answer 30

prompt(title, [default]);

result will equal null. Except in IE, it will equal undefined. Which can cause problems if the following code is looking for a string.

Can help but setting the default to ‘’ (empty string)

Question 31

Get user input boolean in a modal window.

Answer 31

confirm()

Question 32

How do you convert things to Boolean?

Answer 32

!!
Boolean();

Question 33

Evaluate Boolean(‘0’)

Answer 33

true

Question 34

function run() {

var foo = “Foo”;

let bar = “Bar”;

console.log(foo, bar);

{ var moo = “Mooo”;

let baz = “Bazz”;

console.log(moo, baz);

}

console. log(moo);
console. log(baz);

} run();

Answer 34

// Mooo

// ReferenceError

Question 35

What happens with:

let apple = ‘fad’;

apple = ‘qwe’;

What does apple equal?

What happens with:

const pear = ‘fd’

pear = ‘ert’

What does pear equal?

Answer 35

// returns qwe

// error and pear still equals ‘fd’

Question 36

What’s a substitution?

Answer 36

Embedded expression within a string

Template literals are literals delimited with backticks (`), allowing embedded expressions called substitutions.

Question 37

What are three things that happen before line 1 of code is evaluated?

Answer 37

Variables are set aside

Functions declarations are completed

Syntax errors are found (other errors will happen after code is run)

Question 38

Why can’t numbers be variables (or have numbers leading in a variable name like “123a” )?

Answer 38

int a = 2;
int 2 = 5;
int c = 2 * a;

This is confusing so they don’t allow numbers leading in variables

Question 39

What is a ‘reachable’ value?

Answer 39

values that are accessible or usable somehow and are guaranteed to be stored in memory.

Question 40

If a reachable object references another object, it is not automatically reachable as well

T or F

Answer 40

False

Question 41

What distinguishes a root value from a non root value in terms of reachability

Answer 41

If a root object

For instance:

• The currently executing function, its local variables and parameters.
• Other functions on the current chain of nested calls, their local variables and parameters.
• Global variables.
• (there are some other, internal ones as well)

References another value. That other value may be reachable, but is not the root.

Question 42

What is the garbage collector?

Give an example

Answer 42

A background process that monitors all objects and removes that that have become unreachable.

let user = {name: ‘john’}

user = {name: ‘sophi’}

{name:john} still exists, it’s just not referenced and cannot be recovered. The garbage collector looks for these and removes them.

but if we had:

backupOfUser = user;

{name: ‘john’} is still referenced.

Question 43

If an object references another object, but is not referenced itself by a root, it will be removed by the garbage collector

T or F

Answer 43

T

Question 44

If an object is referenced, it will not be removed by the garbage collector

T or F

Answer 44

F

it’s not enough to be referenced. It has to be referenced by some path from a root.

Otherwise it can’t be reached really and the garbage collector assumes it’s not needed.

Question 45

What makes an unreachable object?

(2 ways)

Answer 45

The variable is reassigned somewhere else.

or

A variable is deleted

Question 46

What are the 3 different kinds of control statements?

Answer 46

Conditional/Selection statements
Iteration/Loop statements
Jump statements

Question 47

Difference between src and href?

Answer 47

src brings the content in (images, scripts) and basically dumps the content where the tag is.

href specifies the location of a Web resource. It goes to that resource for information. Like links to other pages and CSS stylesheets.

Question 48

Create a single line comment
Create multi line comment

What is general formatting for multi line comment?

Answer 48

// single line comment

/* multi line comment
** with double stars for in between

** just for show.
*/

Question 49

What happens
console.log(greeting);

var greeting = ‘Hello world!’;

Answer 49

logs undefined
var is hoisted.
equivalent to:
var greeting;

console.log(greeting);

greeting = ‘Hello world!’

Question 50

What happens with this:
function myFunction() {
let a = 1;

if (true) {
console.log(a);
let a = 2;
console.log(a);
}
}

myFunction();

Answer 50

ReferenceError: Cannot access ‘a’ before initialization

Technically, the scope of a is the entire block. JavaScript does hoist the variables defined by let, but, when it does, it creates a “temporal dead zone” in which the variable exists but doesn’t have a value – not even a value of undefined. We talk more about the temporal dead zone in a later course