Backend

Question 1

Es-6-const-let

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

Answer 1

Code blocks are denoted by curly braces. Examples are if else, for, do while, while, try catch and so on.

Question 2

Es-6-const-let

What does block scope mean?

Answer 2

A block scoped variable means that the variable defined within a block will not be accessible from outside the block. A block can reside inside a function, and a block scoped variable will not be available outside the block even if the block is inside a function.

Question 3

Es-6-const-let

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

Answer 3

Block-scope

Question 4

Es-6-const-let

What is the difference between let and const?

Answer 4

The const keyword cannot be reassigned, meaning it creates a read-only reference to a value. But the let keyword is mutable, meaning you can change its values anytime.

Question 5

Es-6-const-let

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

Answer 5

We are not reassigning the value of a variable.

Question 6

Es-6-const-let

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

Answer 6

If you don’t intend to modify the variable, then use the const keyword. Otherwise, use let keyword. Always default const if you are not sure.

Question 7

Es-6-template-literals

What is the syntax for writing a template literal?

Answer 7

Keyword variable name equal sign backticks with text content.

Question 8

Es-6-template-literals

What is “string interpolation”?

Answer 8

String interpolation is replacing placeholders with values in a string literal.

Question 9

Es-6-destructuring

What is destructuring, conceptually?

Question 10

Es-6-destructuring

What is the syntax for Object destructuring?

Question 11

Es-6-destructuring

What is the syntax for Array destructuring?

Question 12

Es-6-destructuring

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

Question 13

Es-6-arrow-functions

What is the syntax for defining an arrow function?

Answer 13

Variable keyword, function name, equal sign, parameters with parenthesis, arrow, function code block with curly braces if there is more than one line
let add = (x, y) => x + y;
let add = (x, y) => {return x + y};

Question 14

Es-6-arrow-functions

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

Answer 14

Implicitly return value

Question 15

Es-6-arrow-functions

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

Answer 15

Refers to window object or global object
Arrow functions do not have their own this.
Whatever this is in the parent scope and it doesn’t create own lexical scope

Question 16

Command-line-basics

What is a CLI?

Answer 16

Command-line interface
A command-line interpreter or command-line processor uses a CLI to receive commands from a user in the form of lines of text. This provides a means of setting parameters for the environment, invoking executables and providing information to them as to what actions they are to perform.

Question 17

Command-line-basics

What is a GUI?

Answer 17

Graphical user Interface.
A GUI is a form of user interface that allows users to interact with electronic devices through graphical icons and audio indicators such as primary notation, instead of text-based UIs, typed command labels or text navigation.

Question 18

Command-line-basics

Give at least one use case for each of the commands listed in this exercise.

Answer 18

1. Man - Show manual page for a command. Look up what a command does
2. Cat - concatenate files and print on the standard output
3. Ls list directory content. - what directories we have
4. Pwd to find out current directory you are in
5. Echo - display line of text/string that passed as an argument
6. Touch create a blank text file, Before creating a text file, it was used to change file access and modification time
7. Mkdir create a new directory(folder)
8. Mv - move a file or folder, but also rename the text
9. Rm permanently remove a file or directory
10. Cp - copy a file and can move to another directory

Question 19

Command-line-basics

What are the three virtues of a great programmer?

Answer 19

1. Laziness: The quality that makes you go to great effort to reduce overall energy expenditure. It makes you write labor-saving programs that other people will find useful and document what you wrote so you don’t have to answer so many questions about it.
2. Impatience: The anger you feel when the computer is being lazy. This makes you write programs that don’t just react to your needs, but actually anticipate them. Or at least pretend to.
3. Hubris: The quality that makes you write (and maintain) programs that other people won’t want to say bad things about.

Question 20

Node-Intro

What is Node.js?

Answer 20

Node.js is a program that allows JavaScript to be run outside of a web browser.

Question 21

Node-Intro

What can Node.js be used for?

Answer 21

Node.js can be used to build back ends for web applications, command-line programs or any kind of automation that developers wish to perform.

Question 22

Node-Intro

What is a REPL?

Answer 22

Read-Evaluate-Print-Loop

Question 23

Node-Intro

When was Node.js created?

Answer 23

May 27, 2009

Question 24

Node-Intro

What back end languages have you heard of?

Answer 24

C++, C#, Ruby, PHP

Question 25

Node-process-argv | What is the process object in a Node.js program?

Answer 25

The process object is a global that provides information about, and control over, the current Node.js process.

Question 26

Node-process-argv | How do you access the process object in a Node.js program?

Answer 26

Type the process

Question 27

Node-process-argv | What is the data type of process.argv in Node.js?

Answer 27

Array

Question 28

Node-module-system | What is a JavaScript module?

Answer 28

It is a single .js file | Each file considers own module

Question 29

Node-module-system | What values are passed into a Node.js module's local scope?

Answer 29

Exports, require, module, __filename, __dirname

Question 30

Node-module-system Give two examples of truly global variables in a Node.js program.

Answer 30

process and console

Question 31

Node-require | What is the purpose of module.exports in a Node.js module?

Answer 31

Assign a value and use it at some other file.

Question 32

``` Node-require How do you import functionality into a Node.js module from another Node.js module? ```

Answer 32

Use require function and call the .js file

Question 33

The-event-loop | What is the JavaScript Event Loop?

Answer 33

Look at the stack and task queue, if the stack is empty, it pushes callback to the stack

Question 34

The-event-loop | What is different between "blocking" and "non-blocking" with respect to how code is executed?

Answer 34

Blocking- slow, block the execution of JavaScript until a certain long task has finished When blocking, prevent anything from happening. Nothing can happen. Non-blocking is the asynchronous that it wouldn’t block and accept call back function Push off to the side so that other codes can work.

Question 35

node-fs-readfile | What is a directory?

Answer 35

Folder that contains multile files

Question 36

node-fs-readfile | What is a relative file path?

Answer 36

file on the current working directory

Question 37

node-fs-readfile | What is an absolute file path?

Answer 37

Root to all the way up to where the file is

Question 38

``` node-fs-readfile What module does Node.js include for manipulating the file system? ```

Answer 38

fs module

Question 39

``` node-fs-writefile What method is available in the Node.js fs module for writing data to a file? ```

Answer 39

fs.wrtieFile method

Question 40

``` node-fs-writefile Are file operations using the fs module synchronous or asynchronous? ```

Answer 40

Asynchronous

Question 41

http-message-recap | What is a client?

Answer 41

Service requester, requests content or service from a server | Program that requests to another program or computer

Question 42

http-message-recap | What is a server?

Answer 42

The provider of a resource or service | The program listening to incoming response

Question 43

http-message-recap | Which HTTP method does a browser issue to a web server when you visit a URL?

Answer 43

GET

Question 44

http-message-recap | What is on the first line of an HTTP request message?

Answer 44

HTTP method 2. The request target 3. The HTTP version

Question 45

http-message-recap | What is on the first line of an HTTP response message?

Answer 45

The protocol version 2. Status code 3. Status text | A typical status line looks like: HTTP/1.1 404 Not Found.

Question 46

http-message-recap | What are HTTP headers?

Answer 46

General headers, response headers, representation headers HTTP headers let the client and the server pass additional information with an HTTP request or response. An HTTP header consists of its case-insensitive name followed by a colon (:), then by its value. Whitespace before the value is ignored.

Question 47

http-message-recap Is a body required for a valid HTTP message?

Answer 47

No, not all requests have one: requests fetching sources like GET, HEAD, DELETE or OPTIONS, usually don’t need one. BUT some requests send data to the server in order to update it: as often the case with POST requests (containing HTML form data).

Question 48

npm-intro | What is NPM?

Answer 48

Package manager for JavaScript Reeuse codes from other developers and share codes npm is the world’s largest software registry npm consists: the website, the command line interface(CLI) and the registry

Question 49

npm-intro What is a package?

Answer 49

Directory with one or more files in it. | Collection of files that are together to make up single program/library

Question 50

npm-intro How can you create a package.json with npm?

Answer 50

npm init —yes (default for setting)

Question 51

npm-intro What is a dependency and how to you add one to a package?

Answer 51

Dependencies are specified in a simple object that maps a package name to a version range. You can add one to a package by npm i package name

Question 52

npm-intro What happens when you add a dependency to a package with npm?

Answer 52

You get node_modules with jquery

Question 53

Express-intro | How do you add express to your package dependencies?

Answer 53

npm i express

Question 54

Express-intro What Express application method starts the server and binds it to a network PORT?

Answer 54

listen() method

Question 55

express-hello-world | How do you mount a middleware with an Express application?

Answer 55

Use method With optional mount path. ‘/user/:id’ The path for which the middleware function is invoked;

Question 56

express-hello-world Which objects does an Express application pass to your middleware to manage the request/response lifecycle of the server?

Answer 56

``` Call back method Request object(req), response object(res) and the next middleware function(next) ```

Question 57

express-get-json | What is the appropriate Content-Type header for HTTP messages that contain JSON in their bodies?

Answer 57

application/json

Question 58

express-delete What is the significance of an HTTP request's method?

Answer 58

HTTP defines a set of request methods to indicate the desired action to be performed for a given resource. Although they can also be nouns, these request methods are sometimes referred to as HTTP verbs.

Question 59

express-post-json What does the express.json() middleware do and when would you need it?

Answer 59

express.json() returns a middleware that only parses JSON and only looks at request where the Content-Type header matches the type option. This parser accepts Parse incoming base body, Needed when send data to the server

Question 60

postgres-intro What is PostgreSQL and what are some alternative relational databases?

Answer 60

PostgreSQL is a powerful, open source object-relational database system Other popular relational databases include MySQL, SQL Server by Microsoft, and Oracle by Oracle Corporation

Question 61

postgres-intro What are some advantages of learning a relational database?

Answer 61

If you are storing related data, then a relational database is probably a good first choice. A quality of many relational databases is that they support good guarantees about data integrity. They can store and modify data in a way that makes data corruption as unlikely as possible. This means that developers can set up their database to reject “bad” data and not worry about data being “half written”.

Question 62

postgres-intro What is one way to see if PostgreSQL is running?

Answer 62

Sudo service postgresql status

Question 63

postgres-database What is a database schema?

Answer 63

A collection of tables is called a schema. A schema defines how the data in a relational database should be organized.

Question 64

postgres-database What is a table?

Answer 64

A table is a list of rows like a spreadsheet where each row is a record in that spreadsheet. The Table is made of columns and rows and each row has the same set of attributes.

Question 65

postgres-database What is a row?

Answer 65

Row has the same set of attributes | Row is where the data is stored.

Question 66

SQL-select What is SQL and how is it different from languages like JavaScript?

Answer 66

SQL is Structured Query Language. SQL interact with database. SQL is a declarative programming language. In declarative languages, programmers describe the results they want and the programming environment comes up with its own plan for getting those results unlinke JavaScript which is imperative programming language that basically programers tell the JavaScript runtime what to do and how to do it .

Question 67

SQL-select How do you retrieve specific columns from a database table?

Answer 67

1. The query starts with the select keyword 2. The select keyword is followed by a comma-separated list of column names, each surrounded by “ double quotes. 3. The column names are followed by a from clause specifying which table to retrieve the data from. 4. The query must end in a ; semicolon

Question 68

SQL-select How do you filter rows based on some specific criteria?

Answer 68

where clause 1. The where clause comes after the from clause 2. The where clause is checking the “category” of each row in the table 3. Text value, such as ‘cleaning’ are wrapped in a single quote. Not double quotes! 4. The value of the text value column is being compared using a single = equal sign.

Question 69

SQL-select What are the benefits of formatting your SQL?

Answer 69

Makes it easier to read, maintain, and edit

Question 70

SQL-select What are four comparison operators that can be used in a where clause?

Answer 70

Equal sign(=), greater than(>), less than (>), and not equal to sign (!=)

Question 71

SQL-select How do you limit the number of rows returned in a result set?

Answer 71

1. The limit clause comes last 2. The limit clause includes a literal integer number with no quote to specify the maximum number of rows that should be returned

Question 72

SQL-select How do you retrieve all columns from a database table?

Answer 72

The * asterisk is followed by the select keyword

Question 73

SQL-select How do you control the sort order of a result set?

Answer 73

1. The order by clause comes after the from clause. 2. The order by clause is followed by a column name in " double quotes. 3. The default sort order of the results is ascending order.

Question 74

SQL - Insert | How do you add a row to a SQL table?

Answer 74

Use insert statement to add rows to a table

Question 75

SQL - Insert What is a tuple?

Answer 75

A tuple is a list of values

Question 76

SQL - Insert How do you add multiple rows to a SQL table at once?

Answer 76

Separate more than one tuple of values separated by comma

Question 77

SQL - Insert How do you get back the row being inserted into a table without a separate select statement?

Answer 77

Returning clause with * asterisk | Returning only works with insert, update and delete

Question 78

SQL-Update | How do you update rows in a database table?

Answer 78

Use update statment and set column to value and specify where(which one)

Question 79

SQL-Update Why is it important to include a where clause in your update statements?

Answer 79

Because if we don’t put the where clause to specify which one to update, every row will be updated with the same value.

Question 80

SQL-Delete | How do you delete rows from a database table?

Answer 80

Delete statement where clause and returning clause

Question 81

SQL-Delete How do you accidentally delete all rows from a table?

Answer 81

Delete from table name and don’t specify which row you want to delete not indicating where clause

Question 82

SQL-Join | What is a foreign key?

Answer 82

Instead of putting all information into one row, use one column that links two different SQL tables Any columns that link tables together

Question 83

SQL-Join | How do you join two SQL tables?

Answer 83

Join clause

Question 84

SQL-Join | How do you temporarily rename columns or tables in a SQL statement?

Answer 84

Table name as keyword rename in the from and join clauses

Question 85

SQL-Aggregates | What are some examples of aggregate functions?

Answer 85

max(), avg(), count(), min(), sum(), every()

Question 86

SQL-Aggregates | What is the purpose of a group by clause?

Answer 86

The purpose is to separate rows into groups and perform aggregate function on those groups of rows.

Question 87

es6-Promises | What are the three states a Promise can be in?

Answer 87

Pending: initial state, neither fulfilled nor rejected Fulfilled: meaning that the operation was completed successfully Rejected: meaning that the operation failed

Question 88

es6-Promises | How do you handle the fulfillment of a Promise?

Answer 88

Then method passing resolve callback function with resolve value

Question 89

es6-Promises | How do you handle the rejection of a Promise?

Answer 89

Catch method passing reject callback function with rejec value, error object

Question 90

Array-filter | What is Array.prototype.filter useful for?

Answer 90

Filter in array and get a new array with filtered out result. Does not affect the original array

Question 91

Array-map | What is Array.prototype.map useful for?

Answer 91

The map()method creates a new array populated with the results of calling a provided function on every element in the calling array.

Question 92

Array-reduce | What is Array.prototype.reduce useful for?

Answer 92

The reduce() method is used to calculate a single value from an array. In other terms, the reduce() method reduces an array into a single value.