Preparations

Question 1

What is a runtime environment?

Answer 1

It is an execution environment that lets an application program access system resources and provides the tools the application needs to operate.

Question 2

What is a runtime environment in simple words?

Answer 2

It turns an application from a set of instructions into something that performs actual work.

Question 3

What is a programming language?

Answer 3

A programming language is a set of syntactic and semantic rules that describe a formal language and must be able to express the steps that a machine needs to perform to convert some input to an output.

Question 4

Before the computer can perform those steps, what does it need to happen?

Answer 4

The program needs to be converted to a form the computer can understand.

Question 5

What programs do we need for this conversion?

Answer 5

Compilers and interpreters.

Question 6

What do compilers and interpreters do?

Answer 6

At their most basic level, compilers and interpreters are similar: they both translate a program written in a specific programming language to something that the computer can execute, typically referred to as “1s and 0s” since all information on digital computers gets stored as 1s and 0s.

Question 7

How do compilers and interpreters differ?

Answer 7

They differ primarily in what they do with those 1s and 0s.

Question 8

What do compilers do?

Answer 8

Compilers produce an output file that the computer can run directly, perhaps after some additional processing called linking.

Question 9

What do interpreters do?

Answer 9

Interpreters, however, don’t produce 1s and 0s that the computer can run directly - instead, the interpreter runs the interpreted code directly, or perhaps passes it on to a companion program.

Question 10

Is JavaScript an interpreted language?

Answer 10

YES!

However, for performance reasons, most modern JavaScript engines employ a special kind of compiler called a Just In Time (JIT) compiler that takes the interpreted code one step further and lets the computer run the result.

Question 11

What does an Application Programming Interface (API) do?

Answer 11

When an application accesses an operating system’s resources, something must ensure that the operating system provides them in a regulated and safe manner.
The API provides that functionality.

Question 12

What does an API do in other terms?

Answer 12

It describes the scheme and format that a programmer can use to securely access resources, with the operating system acting as an intermediary.

Question 13

What does a runtime environment do?

Answer 13

A runtime environment typically adds another layer of abstraction on top of the operating system’s API to make these resources available with a higher-level (i.e., more accessible) API.

Question 14

What is a runtime environment composed of?

Answer 14

The compiler/interpreter and the operating system’s APIs together make up a runtime environment.

In other words, they provide the tools that an application needs to run.

Question 15

What is a development environment?

Answer 15

A runtime environment with debugging and profiling tools.

For our purposes, we’ll treat the developer tools as part of the runtime environment.

Question 16

What are the two major runtime environments in JavaScript?

Answer 16

The browser and Node.js.

Question 17

What is the browser?

Answer 17

The web browser was the original JavaScript runtime environment, and it’s still the most dominant.

JavaScript running in the browser is far more ubiquitous than JavaScript running anywhere else.

Almost every browser has a JavaScript engine built into it.

Question 18

What are the two main purposed of the browser?

Answer 18

1) to programmatically alter web pages based on user actions.

2) to exchange messages with a server over a network.

Question 19

What does the programmer need to alter web pages?

Answer 19

The programmer needs an API through which they can manipulate the structure and appearance of the HTML page.

The DOM (Document Object Model) API lets you manipulate the structure and appearance of a web page

Question 20

What does the programmer need to exchange messages with a server over a network?

Answer 20

The XHR (XMLHttpRequest) interface and the Fetch API let you communicate with a server.

Question 21

Do browsers have developer tools?

Answer 21

All major browsers provide a “Developer Tools” feature that includes a REPL, a debugger, a network inspector, a performance profiler, and more.

Question 22

What is Node.js?

Answer 22

Node.js is a runtime environment that turns JavaScript into a general-purpose programming language that can run applications on almost any system.

Question 23

What is Node.js composed of?

Answer 23

The creators of Node.js took the open-source Chrome V8 JavaScript engine and added APIs and tools required for desktop and server computing.

It also provides an interactive REPL (read-eval-print loop) where you can execute JavaScript commands and get instant results.

Question 24

What capabilities does a general-purpose programming language (like Node.js) require?

Answer 24

1. The ability to read and write disk files (disk I/O)
2. The ability to read and write via the terminal (standard I/O)
3. The ability to send and receive messages over a network (network I/O)
4. The ability to interact with a database.

Question 25

What is a code editor used for?

Answer 25

A code editor is used to create plain text documents with no styling or formatting.

Question 26

How do I use the semicolons?

Answer 26

Use semicolons to terminate each logical line of code unless the line ends with {, }, or :

Question 27

When should I use camelCase?

Answer 27

Use camelCase formatting for most variable and function names.

Question 28

When should I use PascalCase?

Answer 28

Constructor functions

Question 29

When should I use uppercase names with underscores (SCREAMING_SNAKE_CASE)?

Answer 29

1. To represent constants that serve as unchanging configuration values in your program.
2. TO represent so-called magic numbers (which may not actually be numbers) – constants that are important to your program in some way but not as configuration values. For instance:

Question 30

What are the simple commands in the command line?

Answer 30

Question 31

What is a REPL?

Answer 31

A REPL (read-eval-print loop) for a programming language is an interactive environment where you can type commands and expressions in that language and get immediate results. Node.js comes with one such REPL, which you access with the node command:

Question 32

Should you test code in ‘node’?

Answer 32

YES!

With the REPL, it’s easy to confirm whether some code works as you expect, and it can help you figure out how to fix the command if it doesn’t work.

Question 33

What do you type to exit the console and go back to the command line?

Answer 33

Press “control-c” twice, or press “control-d” once.

Question 34

How can you run JavaScript files from the command line?

Answer 34

Once you create a JavaScript file, one with a .js extension, you can run the code in that file by typing the node command followed by the file name.

Question 35

What happens when you run a JavaScript file from the command line, the code gets executed by something called an interpreter?

Answer 35

The code gets executed by something called an interpreter: it takes JavaScript code and turns it into code that your computer understands.

Question 36

What do you write to exit a program?

Answer 36

“control + c”

Question 37

How do you run code from a file in a browser?

Answer 37

1. You must first embed the code in an HTML file
2. Add a script tag to the HTML file that has the path to your .js file in the src attribute.
3. Save the HTML file, then open it in a browser. You should see a blank page in your browser. To see the JavaScript output, you must visit the console, which we’ll describe in the next section.

Question 38

What is another way to run code from a file in a browser?

Answer 38

It is to write all your JavaScript between the opening and closing

 tags: don't use a .js file at all.

Question 39

What does a programming environment provide?

Answer 39

A programming environment provides two main types of reusable code to an application:

1) components and operations that are part of the core language, often collectively referred to as the standard library.

2) components and operations specific to a runtime environment.

Question 40

What are constructors?

Answer 40

Factories that create values of a particular type

Question 41

What are methods in JavaScript?

Answer 41

Methods are functions that need a value that you can use to call the function.

Question 42

How many types of methods are there?

Answer 42

There are two types of methods:

1. Instance methods
2. Static methods

Question 43

What format do you use to call instance methods?

Answer 43

Constructor.prototype.methodName()

Question 44

What format do you use to call static methods?

Answer 44

Constructor.methodName()

Question 45

As well as operations, what do some data types have?

Answer 45

Properties

A data type’s property is a noun; an operation is a verb.

A property name says something about the value and an operation does something with that value.

Question 46

What do you apply instance methods to?

Answer 46

To a value of the type that the constructor represents.

Question 47

How do you call static methods?

Answer 47

You use the constructor name (String) instead of a value