Basic JS

Question 1

Javascript is dynamically typed, what does that mean?

Answer 1

We can put any type in a variable. For example, a variable can at one moment be a string and then store a number:

Question 2

What does the number type represent?

Answer 2

Both integer and floating point numbers.

Question 3

Besides regular numbers, there are so-called “special numeric values” which also belong to the number data type, what are they ?

Answer 3

Infinity, -Infinity and NaN.

Question 4

NaN is sticky. What does that mean?

Answer 4

Any further mathematical operation on NaN returns NaN:

Question 5

What is the largest value the “number” type can safely represent?

Answer 5

((2^53)-1)

Question 6

BigInt type was recently added to the language to represent integers of arbitrary length. How do you define a BigIng value?

Answer 6

A BigInt value is created by appending n to the end of an integer.

Question 7

What can we do with backticks in Javascript?

Answer 7

Backticks are “extended functionality” quotes. They allow us to embed variables and expressions into a string by wrapping them in ${…}.

Question 8

Is there a char in Javascript?

Answer 8

No, There is no character type.

Question 9

What type does the null value belong to ?

Answer 9

It forms a separate type of its own which contains only the null value:

Question 10

What is the meaning of null ?

Answer 10

It’s just a special value which represents “nothing”, “empty” or “value unknown”.

Question 11

What is the meaning of undefinedl ?

Answer 11

The meaning of undefined is “value is not assigned”. If a variable is declared, but not assigned, then its value is undefined:

Question 12

What is the The typeof operator and what does it do ?

Answer 12

The typeof operator returns the type of the operand. It’s useful when we want to process values of different types differently or just want to do a quick check.

Question 13

What happens when we try to concatenate a string and a number?

Answer 13

You might expect this to return an error, but it works just fine. How numbers should be displayed as strings is fairly well-defined, so the browser automatically converts the number to a string and concatenates the two strings.

Question 14

If we have a numeric variable that we want to convert to a string, we can use ?

Answer 14

The String() function converts its argument to a string.

Question 15

If we have a string that we want to convert to a numeric variable, we can use ?

Answer 15

The Number() function converts anything passed to it into a number, if it can.

Question 16

The length property returns ?

Answer 16

The length of a string

Question 17

There are 3 methods for extracting a part of a string, what are they ?

Answer 17

slice(start, end)
substring(start, end)
substr(start, length)

Question 18

How do open dev tools on keyboard?

Answer 18

opt, commmand, c

Question 19

What are return values?

Answer 19

The values that a function returns when it completes

Question 20

What are parameters,in Javascript functions?

Answer 20

In JavaScript, parameters are the items listed between the parentheses in the function declaration.

Question 21

What are arguments, in Javascript functions?

Answer 21

Function arguments are the actual values we decide to pass to the function.

Question 22

How is a function build up?

Answer 22

The function keyword goes first, then goes the name of the function, then a list of parameters between the parentheses (comma-separated, empty in the example above, we’ll see examples later) and finally the code of the function, also named “the function body”, between curly braces.

Question 23

What does a function with an empty return or without returns, return?

Answer 23

Undefined

Question 24

Never add a newline between return and the value, why?

Answer 24

because JavaScript assumes a semicolon after return

Question 25

One function – one action

Answer 25

A function should do exactly what is suggested by its name, no more.

Question 26

What is a Function Expression?

Answer 26

a function, created inside an expression or inside another syntax construct.

It allows us to create a new function in the middle of any expression.

Question 27

In JavaScript, a function is a value

Question 28

What is a callback function?

Answer 28

The idea is that we pass a function and expect it to be “called back” later if necessary.

Question 29

When is a function expression created?

Answer 29

A Function Expression is created when the execution reaches it and is usable only from that moment.

Question 30

When can we call a function declaration ?

Answer 30

Always, A Function Declaration can be called earlier than it is defined.

Question 31

Another special feature of Function Declarations is their block scope. What is that ?

Answer 31

n strict mode, when a Function Declaration is within a code block, it’s visible everywhere inside that block. But not outside of it.

Question 32

How do arrow functions look like?

Answer 32

let func = (arg1, arg2, …, argN) => expression;

Question 33

What is a call stack?

Answer 33

A call stack is a way for the JavaScript engine to keep track of its place in code that calls multiple functions. It has the information on what function is currently being run and what functions are invoked from within that function

Question 34

The call stack works based on the WHICH principle?

Answer 34

The call stack works based on the last-in-first-out (LIFO) principle.

Question 35

What is A ReferenceError?

Answer 35

A ReferenceError is thrown when one refers to a variable that is not declared and/or initialized within the current scope.

Question 36

What is a Syntax error?

Answer 36

A syntax error occurs when the code you are trying to run is not written correctly, i.e., in accordance with the grammatical rules of JavaScript.

Question 37

When is a Type error thrown ?

Answer 37

an operand or argument passed to a function is incompatible with the type expected by that operator or function;
or when attempting to modify a value that cannot be changed;
or when attempting to use a value in an inappropriate way.

Question 38

What is the DOM ?

Answer 38

The DOM (or Document Object Model) is a tree-like representation of the contents of a webpage - a tree of “nodes” with different relationships depending on how they’re arranged in the HTML document.

Question 39

What selectors could I use to refer to <div class="display"></div>?

Answer 39

div.display
.display
#container > .display
div#container > div.display

Question 40

What does element.querySelector(selector) do ?

Answer 40

returns a reference to the first match of selector.

Question 41

What does element.querySelectorAll(selectors) do ?

Answer 41

returns a “nodelist” containing references to all of the matches of the selectors.

Question 42

What is a callback?

Answer 42

Callbacks are functions that are passed into another function as an argument.

Question 42

Arrow Functions are shorter way to write a function. What are the rules of arrow functions ?

Answer 42

If there is only one argument, the parenthesis () can be omitted
if arrow functions are one line, the brackets {} can be omitted.
When omitting the brackets, the arrow function returns the evaluated expression without requiring the return keyword.

Question 43

Shorten this with the arrow function rules :

const playThe = (funky) => {
return funky + “ music”;
}

Answer 43

const playThe = funky => funky + “ music”;

Question 44

How to switch branches on git?

Answer 44

git checkout <branch_name></branch_name>

Question 44

How to make a new branch on git?

Answer 44

git branch <branch_name></branch_name>

Question 45

How to create a new branch and switch right to it ?

Answer 45

git checkout -b <branch_name></branch_name>

Question 46

How to see all current branches?

Answer 46

git branch

Question 47

How to go back to main branch ?

Answer 47

git checkout main

Question 48

How to merge ?

Answer 48

git merge <branch_name> which will take the changes you’ve committed in branch_name and add them to the branch that you’re currently on.</branch_name>