PB

Question 1

What are the differences between objects and arrays? What is the purpose of the object and what is the purpose of the array?

Answer 1

• An object can store multiple properties with key names, while an array can store a list of items that are usually of the same type (e.g., all numbers or all strings).
• You can access an object’s property using the property’s key name, while you access an array’s element using its index.
• Objects are typically used to store properties that describe something, like the attributes of a book (name, author, price, etc.).
• Arrays are commonly used to store lists of data, like a group of ages or a collection of objects (e.g., books).

Question 2

• How can you access a key’s value in an object?

Answer 2

• There are two ways:
  - objectName.keyName
  - objectName["keyName"]

Question 3

• How can you access the first and the last item of an array? (JS)

Answer 3

• First element: arrayName[0]
• Last element: arrayName[arrayName.length - 1]

Question 4

• Name all the primitive types in JavaScript.

Answer 4

• number, bigint, string, boolean, undefined, null, symbol

Question 5

• What are the assignment operators? Name some of them.

Answer 5

• Assignment (=)
• Addition assignment (+=)
• Subtraction assignment (-=)
• Multiplication assignment (*=)
• Division assignment (/=)
• Modulus assignment (%=)
• Exponentiation assignment (**=)

Question 6

• What are the arithmetic operators? Name some of them.

Answer 6

• Addition (+)
• Subtraction (-)
• Multiplication (*)
• Division (/)
• Modulus (%)
• Increment (++)
• Decrement (--)
• Exponentiation (**)

Question 7

• What are the comparison operators? Name some of them.(JS)

Answer 7

• Equal to (==)
• Strict equal to (===)
• Less than (<)
• Greater than (>)
• Less than or equal to (<=)
• Greater than or equal to (>=)
• Not equal (!=)
• Not equal value or type (!==)

Question 8

• What are the logical operators? Name some of them.

Answer 8

• And (&&)
• Or (||)
• Not (!)

Question 9

• What is the difference between for, for of and for in?

Answer 9

• for is a loop used to execute a block of code a certain number of times.
• for...of loops through the values of iterable objects like arrays, strings, sets, and maps.
• for...in loops through the properties of an object.

Question 10

• How do you find the average of values in an array if you can’t use any built-in functions or methods?

Answer 10

let sum = 0;
for (let value of array) {
  sum += value;
}
let average = sum / array.length;

Question 11

• What are the main parts of a function?

Answer 11

• Parameters, the function body, and arguments.

Question 12

• What is the difference between parameters and arguments?

Answer 12

• Parameters are placeholders in the function’s declaration, while arguments are the actual values passed to the function when it’s called.

Question 13

• What are the differences between function expression and function statement?

Answer 13

• Function expression: var foo = function() {...};
• Function declaration: function foo() {...};
• Function declarations are hoisted and can be used before their declaration. Function expressions are not hoisted and can’t be used before their declaration.

Question 14

• What is a method?

Answer 14

• A method is a function that belongs to an object or a class.

Question 15

• Name 3 builtin functions (and/or methods) regarding strings.

Answer 15

• str.length
• str.split()
• str.slice()
• Str.repeat()
• Str.search()
• Str.toUpperCase()

Question 16

• Name 3 builtin functions (and/or methods) regarding arrays.(JavaScript)

Answer 16

• arr.length
• arr.slice()
• arr.push()
• Arr.pop()
• Arr.splice()
• Arr.join()
• Arr.indexOf()

Question 17

• Name 3 builtin functions (and/or methods) regarding numbers.

Answer 17

• num.toFixed()
• num.toPrecision()
• Nr.toString()
• Number()
• parseInt()
• parseFloat()

Question 18

• What is a callback function?

Answer 18

• A callback function is a function passed as an argument to another function and is executed after the completion of that function.

Question 19

• What are the differences between for loops and forEach?

Answer 19

• A for loop is a general-purpose loop for iterating over values multiple times.
• forEach is a higher-order function used to iterate over elements of an array and execute a callback function on each element.

Question 20

• What is the difference between JavaScript data structures and JSON data structures?

Answer 20

• JavaScript data structures are in-memory representations of objects, arrays, strings, etc.
• JSON data structures are string representations of data, used for data interchange.

Question 21

• How do you create JavaScript data structure from a JSON file’s data?

Answer 21

import * as fs from "node:fs";
let dataStructure = JSON.parse(fs.readFileSync("fileName.json", "utf8"));

Question 22

• What is the difference between JavaScript data structures and DOM (HTML document) data structures?

Answer 22

• JavaScript data structures are used to store and manipulate data in memory.
• DOM data structures represent the structure of HTML documents and allow manipulation of the document’s content.

Question 23

• What are the steps of changing a HTML element’s content with JavaScript?

Answer 23

• Get the element using getElementById or querySelector.
• Use properties like innerHTML, textContent, or insertAdjacentHTML to modify the content.

Question 24

• What is an event listener?

Answer 24

• An event listener is a built-in function that waits for a specific event to occur on an element and triggers a callback function in response.

Question 25

- What are the steps of changing a HTML element's content when the element clicked?

Answer 25

- Create an event listener using `addEventListener`. - Inside the event listener, modify the element's content using `innerHTML` or other properties.

Question 26

- Inside a `click` event listener, how can you access the element that has been clicked?

Answer 26

- By using the event object passed to the event listener function, often referred to as `event` or `e`.

Question 27

- What are the differences between `display: block` and `display: inline` CSS properties?

Answer 27

- `display: block` makes an element a block-level element, taking up the entire width of its parent and stacking vertically. - `display: inline` makes an element an inline-level element, allowing other elements to sit beside it on the same line.

Question 28

- What are the differences between `position: relative` and `position: absolute` CSS properties?

Answer 28

- `position: relative` positions an element relative to its normal position. - `position: absolute` positions an element relative to its closest positioned ancestor.

Question 29

- What is the box model, name the CSS properties connecting to it?

Answer 29

- The box model describes how elements are rendered in terms of their content, padding, border, and margin. - Related properties: `margin`, `padding`, `border`, `width`, `height`, `box-sizing`.

Question 30

- What CSS properties affect font and text appearance?

Answer 30

- `color`, `font-size`, `font-weight`, `font-family`, `line-height`, `text-align`, `text-transform`.

Question 31

- What are the steps of adding or removing a HTML element's class name?

Answer 31

- Adding: `element.classList.add("className")` - Removing: `element.classList.remove("className")`

Question 32

- Is `null` an object or a primitive?

Answer 32

- It is a primitive value and represents the absence of any value.

Question 33

- What is `undefined`?

Answer 33

- `undefined` is a special value indicating that a variable has been declared but hasn't been assigned a value.

Question 34

- What does it mean that a data type is mutable and what does it mean that it is immutable? Mention some examples.

Answer 34

- Mutable data types can be changed after creation. Examples include arrays and objects. - Immutable data types cannot be changed after creation. Examples include strings and numbers. ``` let mutableArray = [1, 2, 3]; mutableArray[0] = 10; console.log(mutableArray); // Output: [10, 2, 3] ``` ``` let immutableString = "Hello"; immutableString[0] = "W"; // This won't change the string console.log(immutableString); // Output: "Hello" ``` ``` let immutableNumber = 42; immutableNumber = 99; // This reassigns the variable console.log(immutableNumber); // Output: 99 ```

Question 35

- What does it mean that a data type is passed by value and what does it mean that it is passed by reference? Mention some examples.

Answer 35

- Passed by value means that a copy of the value is passed to a function. Primitives are passed by value. - Passed by reference means that a reference to the original value is passed to a function. Objects are passed by reference.

Question 36

- When to use `var`, `let`, and `const`?

Answer 36

- Use `var` for legacy code or when you need function scope (not recommended in modern code). - Use `let` for variables that will be reassigned. - Use `const` for variables that won't be reassigned.

Question 37

- What is hoisting?

Answer 37

- Hoisting is a JavaScript behavior where variable and function declarations are moved to the top of their containing scope during compilation.

Question 38

- What are the advantages of using a version control system?(git)

Answer 38

- Version control helps track changes, collaborate effectively, manage project history, and revert to previous states.

Question 39

- What’s the difference between Git and GitHub?

Answer 39

- Git is a version control system for tracking changes in code. - GitHub is a platform that provides hosting for Git repositories and additional collaboration features.

Question 40

- What are remote repositories in Git?

Answer 40

- Remote repositories are versions of a project that are hosted on a different server.

Question 41

- Why does a merge conflict occur?

Answer 41

- A merge conflict occurs when changes made in two different branches of a repository cannot be automatically merged.

Question 42

- How do you run a JavaScript file in the terminal?

Answer 42

- Use the command: `node .js`

Question 43

- How do you stop a running a command in the terminal?

Answer 43

- Press `Ctrl+C`

Question 44

- How go you get the previous command in the terminal?

Answer 44

- Use the up arrow key or press `Ctrl+R`

Question 45

- How do you got to the current directory's parent directory in the terminal?

Answer 45

- Use the command: `cd ..`