Node.js

Question 1

What can Node.js be used for?

Answer 1

Node. js is primarily used for non-blocking, event-driven servers, due to its single-threaded nature. It’s used for traditional web sites and back-end API services, but was designed with real-time, push-based architectures in mind.

Question 2

What is a REPL?

Answer 2

A read–eval–print loop (REPL), also termed an interactive toplevel or language shell, is a simple interactive computer programming environment that takes single user inputs, executes them, and returns the result to the user; a program written in a REPL environment is executed piecewise.

Question 3

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

Answer 3

Global variable. The process object in Node.js is a global object that can be accessed inside any module without requiring it. There are very few global objects or properties provided in Node.js and process is one of them.

Question 4

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

Answer 4

The process.argv property returns an array containing the command line arguments passed when the Node.js process was launched. // The first element will be process.execPath. See process.argv0 if access to the original value of argv[0] is needed. The second element will be the path to the JavaScript file being executed. The remaining elements will be any additional command line arguments.

Question 5

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

Question 6

What is a JavaScript module?

Answer 6

A module in JavaScript is just a file containing related code. I
n JavaScript, we use the import and export keywords to share and receive functionalities respectively across different modules. The export keyword is used to make a variable, function, class or object accessible to other modules.

Question 7

What values are passed into a Node.js module’s local scope?

Answer 7

The five parameters — exports , require , module , __filename , __dirname are available inside each module in Node. Though these parameters are global to the code within a module yet they are local to the module (because of the function wrapper as explained above).

Question 8

What is different between “blocking” and “non-blocking” with respect to how code is executed?

Answer 8

Blocking code occupied a call stack, and executed synchronously while non-blocking code execute asynchronously.

Question 9

What is the JavaScript Event Loop?

Answer 9

JavaScript has a runtime model based on an event loop, which is responsible for executing the code, collecting and processing events, and executing queued sub-tasks. This model is quite different from models in other languages like C and Java.

Question 10

What is an absolute file path?

Answer 10

path which includes root of the file. starts with a ‘/’

Question 11

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

Answer 11

fs.writeFile(file, data[, options], callback)

Question 12

What is NPM?

Answer 12

npm is the default package manager for the JavaScript runtime environment Node.js.

It consists of a command line client, also called npm, and an online database of public and paid-for private packages, called the npm registry.

/* npm consists of three distinct components:
the website
the Command Line Interface (CLI)
the registry */

Question 13

What is a package (module)?

Answer 13

It is a directory with files in it => package.json and some reusable code

Question 14

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

Answer 14

A dependency is another package that your package needs in order to work. Dependencies are specified in your pubspec.

Question 15

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

Answer 15

A dependency is another package that your package needs in order to work. Dependencies are specified in your pubspec.

Question 16

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

Answer 16

The app. listen() function is used to bind and listen the connections on the specified host and port.

Question 17

Network interface

Answer 17

Network interface is a piece of hardware on a computer that allows network connectivity (internet) evamples wifi card / adapter Lan card or adapter
- each network interface has own its own IP address
LAN: Local Area Network
Every network interface provides 2^16 “ports”
- the default (aka “well-known”) HTTP port is actually 80
- the defalt (aka “well-known”) Https port is actually 443
- any port number below 1024 requires “admin” privileges to use

Question 18

What is the difference between library and framework ?

Answer 18

A library is a code someone wrote (or separate part of your codebase), a library should be reusable. A framework is a specific kind of library. A framework is different from library when is has “inversion of control”
Who calls who? A framework calls YOUR code, a library is called by your code. A framework describes WHEN to call your functions (you don’t cal them).

Answer 19

Middleware functions are functions that have access to the request object (req), the response object (res), and the next middleware function in the application’s request-response cycle. The next middleware function is commonly denoted by a variable named next.

Middleware functions can perform the following tasks:

Execute any code.
Make changes to the request and the response objects.
End the request-response cycle.
Call the next middleware function in the stack.

Question 20

req (short for “request”)

Answer 20

a data model of the HTTP request massage (from the client)

Question 21

res (short for “response”)

Answer 21

a data model of the HTTP request to the client

Question 22

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

Answer 22

json() is a built-in middleware function in Express. This method is used to parse the incoming requests with JSON payloads and is based upon the bodyparser. This method returns the middleware that only parses JSON and only looks at the requests where the content-type header matches the type option.

Question 23

What is the significance of an HTTP request’s method?

Answer 23

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 24

Four kinds of http requests

Answer 24

GET - read
DELETE - dalete
POST - put
PUT - update

Answer 25

A relational database is a collection of data items with pre-defined relationships between them. These items are organized as a set of tables with columns and rows. Tables are used to hold information about the objects to be represented in the database.

//A relational database is a type of database that stores and provides access to data points that are related to one another.

Question 26

What is one way to see if PostgreSQL is running?

Answer 26

Check the status of the postgresql service. You can do this anytime you want to see if Postgres is running.
“sudo service postgresql status”

Question 27

What is PostgreSQL and what are some alternative relational databases?

Answer 27

PostgreSQL is a powerful, free, open source Relational Database Management System (RDBMS). It is often cited as the most advanced open source database of its kind.

Other popular relational databases include MySQL (also free), SQL Server by Microsoft, and Oracle by Oracle Corporation.

Question 28

Top Advantages of Relational Database

Answer 28

• Simple Model. A Relational Database system is the most simple model, as it does not require any complex structuring or querying processes.
• Data Accuracy. In the relational database system, there can be multiple tables related to one another with the use of a primary key and foreign key concepts. This makes the data to be non-repetitive. There is no chance for duplication of data. Hence the accuracy of data in the relational database is more than any other database system.
• Easy Access to Data. In the Relational Database System, there is no pattern or pathway for accessing the data, as to another type of databases can be accessed only by navigating through a tree or a hierarchical model. Anyone who accesses the data can query any table in the relational database. Using join queries and conditional statements one can combine all or any number of related tables in order to fetch the required data.
• Data Integrity. 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.
• Flexibility.
• Normalization.
• High Security.
• Feasible for Future Modifications.

Question 29

What is a database schema?

Answer 29

A database schema defines how data is organized within a relational database; this is inclusive of logical constraints such as, table names, fields, data types, and the relationships between these entities

// A collection of tables is called a schema. A schema defines how the data in a relational database should be organized. In relational databases, you typically have to define your schema up front and the database server will make sure that any data being written to the database conforms to that schema.

Question 30

What is a table?

Answer 30

A table is a collection of related data held in a table format within a database. It consists of columns and rows. In relational databases, and flat file databases, a table is a set of data elements using a model of vertical columns and horizontal rows, the cell being the unit where a row and column intersect.

Question 31

What is a row?

Answer 31

In relational databases, a row is a data record within a table. Each row, which represents a complete record of specific item data, holds different data within the same structure. A row is occasionally referred to as a tuple.

Question 32

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

Answer 32

SQL is a declarative programming language. Declarative programming is when you write your code in such a way that it describes what you want to do, and not how you want to do it. You “declare” your intent and the Web browser does its best to output the desired results according to a predefined set of rules.

Question 33

How do you retrieve specific columns from a database table?

Answer 33

With select statement (specify atribute name).
// Querying a database typically takes the form of a select statement.

Question 34

How do you filter rows based on some specific criteria?

Answer 34

Filtering Results
Sometimes we want to get a subset of all rows in a table. Considering our original table of data, it is possible to specify which rows should be returned. This is done using a where clause.

Question 35

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

Answer 35

=, <, >, and !=

Question 36

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

Answer 36

SQL provides us with the ability to limit the number of rows included in a result set.

Question 37

How do you retrieve all columns from a database table?

Answer 37

To select all of the columns in a table by replacing the list of column names with an * asterisk

Question 38

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

Answer 38

With “order by” clause in the select statement to control the order of the result set. The default sort order of the results is ascending order.

Question 39

What is a tuple?

Answer 39

In a relational database, a tuple is one record (one row). See record and relational database. A set of values passed from one programming language to another application program or to a system program such as the operating system.

Question 40

How do you add a row to a SQL table?

Answer 40

To add a row to this table, we would likely execute the following command:

insert into “table name” (“attribute name”, “attribute name”)
values (‘values, ‘values).

Question 41

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

Answer 41

insert into “table name” (“attribute name”, “attribute name”), (“attribute name”, “attribute name”)
values (‘values, ‘values), (‘values, ‘values);

Question 42

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

Answer 42

With returning * statement

Question 43

How do you update rows in a database table?

Answer 43

With SQL update statement.
update “table name”
set “attribute” = ‘value’
where “attribute” = ‘value’; (include a where clause in your update statements to only target specific rows)

Question 44

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

Answer 44

If “where” is not included, it would update every row in the table

Question 45

How do you delete rows from a database table?

Answer 45

With SQL delete statement.
delete from “table name”
where “attribute” = ‘value’
and “attribute” < value
returning *;

Question 46

How do you accidentally delete all rows from a table?

Answer 46

delete from “table name”;
If you don’t target specific rows to delete by including a where clause.

Question 47

What is a foreign key?

Answer 47

A foreign key is a set of attributes in a table that refers to the primary key of another table. The foreign key links these two tables.

Question 48

How do you join two SQL tables?

Answer 48

select ..
from “table name1”
join “table name2” using (“column1//key”);

from “table name1”
join “table name2” on “table name1”.”column1” = “table name2”.”column1”

Question 49

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

Answer 49

renaming them just for the result set using the as keyword

select “p”.”name” as “product”,
“p”.”category”,
“s”.”name” as “supplier”,
“s”.”state”
from “products” as “p”
join “suppliers” as “s” using (“supplierId”);

Question 50

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

Answer 50

renaming them just for the result set using the as keyword

select “p”.”name” as “product”,
“p”.”category”,
“s”.”name” as “supplier”,
“s”.”state”
from “products” as “p”
join “suppliers” as “s” using (“supplierId”);

Question 51

What are some examples of aggregate functions?

Answer 51

max(), count() - to count rows, min(), sum(), and every()

Question 52

What is the purpose of a group by clause?

Answer 52

To separate rows into groups and perform aggregate functions on those groups of rows. This is done with a group by clause.

Question 53

What are the three states a Promise can be in?

Answer 53

A Promise is in one of these states:

pending: initial state, neither fulfilled nor rejected.
fulfilled: meaning that the operation was completed successfully.
rejected: meaning that the operation failed.

Question 54

How do you handle the fulfillment of a Promise?

Answer 54

The then() method returns a Promise. It takes up to two arguments: callback functions for the success and failure cases of the Promise.

// Fulfilled is a state of a Promise. It means that the promise has been resolved and now has its resolved value (using the internal resolve function). The operation represented by the promise has been completed successfully.

Question 55

How do you handle the rejection of a Promise?

Answer 55

We must handle the promise rejection. We do so using the catch() method of the promise:
thePromise
.catch(error => {
console.error(error)
})
We must always add a catch(), otherwise promises will silently fail.

Question 56

What does the join() method of Node’s path module do?

Answer 56

The path.join() method joins all given path segments together using the platform-specific separator as a delimiter, then normalizes the resulting path.

Question 57

What does express.static() return?

Answer 57

Parameters: The root parameter describes the root directory from which to serve static assets. Return Value: It returns an Object. OR returns an HTTP 404 if it can’t find a file

Question 58

What is the local __dirname variable in a Node.js module?

Answer 58

The directory name of the current module
__dirname is an environment variable that tells you the absolute path of the directory containing the currently executing file.