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Web Development > JavaScript > Flashcards

JavaScript Flashcards

1
Q

How do you deserialize a JSON string into a data structure using Java
Script?

A

To Deserialize a JSON into a JavaScript object, here we will use a common method JSON.parse() method.

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2
Q

How do you serialize a data structure into a JSON string using JavaScript?

A

The JSON.stringify() method converts a JavaScript object or value to a JSON string, optionally replacing values if a replacer function is specified or optionally including only the specified properties if a replacer array is specified.

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3
Q

What are serialization and deserialization?

A

Serialization is a mechanism of converting the state of an object into a byte stream. Deserialization is the reverse process where the byte stream is used to recreate the actual Java object in memory. This mechanism is used to persist the object.

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4
Q

What is JSON?

A

JavaScript Object Notation (JSON) is a standard text-based format for representing structured data based on JavaScript object syntax.

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5
Q

If you didn’t use a loop to conditionally show or hide the views in the page, how would your JavaScript code be written instead?

A

We would have to add an if statement for every tab loop well loops through everything
String being assigned to the classname property of the tabs object at tabsindex

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6
Q

If you were to add another tab and view to your HTML, but you didn’t use event delegation, how would your JavaScript code be written instead?

A

Need to do query selector for each individual tab rather than query selector all

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7
Q

How can you retrieve the value of an element’s attribute?

A

To get the value of an attribute on a specified element, you call the getAttribute() method of the element:

let value = element.getAttribute(name);

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8
Q

What does the element.matches() method take as an argument and what does it return?

A

The matches() method checks to see if the Element would be selected by the provided selectorString – in other words – checks if the element “is” the selector.

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9
Q

What is the affect of setting an element to display: none?

A

display: none; When you set the value of display to none, the affected element will disappear

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10
Q

If you wanted to insert new clickable DOM elements into the page using JavaScript, how could you avoid adding an event listener to every new element individually?

A

addEventlistener on the parent element

Clicktarget put in a common element and just listen for clicks on

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11
Q

How can you remove an element from the DOM?

A

The Element.remove() method removes the element from the tree it belongs to.

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12
Q

What does the element.closest() method take as its argument and what does it return?

A

The closest() method traverses the Element and its parents (heading toward the document root) until it finds a node that matches the provided selector string. Will return itself or the matching ancestor. If no such element exists, it returns null

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13
Q

What DOM element property tells you what type of element it is?

A

Event.target same thing as querySelector elements have a tagName property

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14
Q

Why is it possible to listen for events on one element that actually happen its descendent elements?

A

Due to event flow the event bubbles

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15
Q

What is the event.target?

A

event.target returns the DOM element that triggered an specific event, so we can retrieve any property/ attribute that has a value.

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16
Q

When does the ‘beforeunload’ event fire on the window object?

A

its resources are about to be unloaded

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17
Q

What data type can localStorage save in the browser?

A

string

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18
Q

How to you retrieve data from localStorage?

A

getItem()

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19
Q

How do you store data localStorage

A

setItem()

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20
Q

What is the purpose of variables?

A

Variables are containers for storing data (storing data values).

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21
Q

How do you initialize (assign a value to) a variable?

A

In JavaScript, the equal sign (=) is an “assignment” operator

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22
Q

What is the purpose of a string?

A

JavaScript strings are for storing and manipulating text. A JavaScript string is zero or more characters written inside quotes.

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23
Q

What is the purpose of a number?

A

Number is a primitive wrapper object used to represent and manipulate numbers like 37 or -9.25 . The Number constructor contains constants and methods for working with numbers.

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24
Q

What is the purpose of a boolean?

A

Boolean is a datatype that returns either of two values i.e. true or false. In JavaScript, Boolean is used as a function to get the value of a variable, object, conditions, expressions, etc. in terms of true or false

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25
Q

What does the = operator mean in JavaScript?

A

Assignment

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26
Q

What is the difference between null and undefined?

A

In JavaScript, undefined means a variable has been declared but has not yet been assigned a value

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27
Q

Why is it a good habit to include “labels” when you log values to the browser

A

Organization

clarity

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28
Q

Give five examples of JavaScript primitives.

A

undefined, null, boolean, string and number

29
Q

What data type is returned by an arithmetic operation?

A

single numerical value

30
Q

What is string concatenation?

A

The JavaScript concatenation operator is a plus sign (+). This operator lets you add the contents of two or more strings together to create one

31
Q

What purpose(s) does the + plus operator serve in JavaScript?

A

The + operator is used to perform both addition and string concatenation in JavaScript

32
Q

What data type is returned by comparing two values (, ===, etc)?

A

Comparison operators — operators that compare values and return true or false

33
Q

What does the += “plus-equals” operator do?

A

The plus-equals operator ( += ) adds the value on the right, to the variable on the left, and then assigns that value back into the variable on the left

34
Q

What are object properties?

A

property is an association between a name (or key) and a value.

35
Q

Describe object literal notation.

A

Object property value

36
Q

How do you remove a property from an object?

A

delete.property

37
Q

How do you calculate the last index of an array?

A

Object.length-1 students[students.length - 1]

38
Q

What is the length property of an array?

A

Stores a count of how many items are in an array

39
Q

How do you calculate the last index of an array?

A

Object.length-1 students[students.length - 1]

40
Q

Why do we log things to the console?

A

The console.log() method outputs a message to the web console

41
Q

What is a method?

A

A method is a function which is a property of an object. There are two kind of methods: Instance Methods which are built-in tasks performed by an object instance, or Static Methods which are tasks that are called directly on an object constructor.

42
Q

How do you remove the last element from an array?How do you round a number down to the nearest integer?How do you round a number down to the nearest integer?

A

pop() method.

43
Q

How do you generate a random number?

A

Math.random()

44
Q

How do you delete an element from an array?

A

The splice() method changes the contents of an array by removing or replacing existing elements and/or adding new elements in place

45
Q

How do you append an element to an array?

A

1) The push() method adds one or more elements to the end of an array and returns the new length of the array. …
2) The unshift() method adds one or more elements to the beginning of an array and returns the new length of the array: var a = [1, 2, 3]; a.

46
Q

How do you break a string up into an array?

A

The split() method

47
Q

Do string methods change the original string? How would you check if you
weren’t sure?

A

No they don’t

48
Q

Roughly how many string methods are there according to the MDN Web docs?

A

38ish

49
Q

Is the return value of a function or method useful in every situation?

A

No ,ex push gives return value that is not needed length may not be needed at the moment

50
Q

Roughly how many array methods are there according to the MDN Web docs?

A

50ish

51
Q

What three-letter acronym should you always include in your Google search about a JavaScript method or CSS property?

A

MDN

52
Q

Give 6 examples of comparison operators.

A

,>=,<=, ===,!==

53
Q

What data type do comparison expressions evaluate to?

A

single Boolean value of either True or False

54
Q

Is else required in order to use an if statement?

A

no

55
Q

Describe the syntax (structure) of an if statement.

A

check the expression to see whether a condition is met and returns a value based on the output obtained

56
Q

What are the three logical operators?

A

||,&&, !

57
Q

How do you compare two different expressions in the same condition?

A

Logical oeprators

58
Q

What is the purpose of a loop?

A

to repeat the same, or similar, code a number of times

59
Q

What is the purpose of a condition expression in a loop?

A

the stopping/breaks of an expression of the loop

60
Q

What does “iteration” mean in the context of loops?

A

number of times loop will be repeated

61
Q

What does “iteration” mean in the context of loops?

A

number of times loop will be repeated

62
Q

When does the condition expression of a while loop get evaluated?

A

each loop iteration

63
Q

When does the initialization expression of a for loop get evaluated?

A

as the loop begins

64
Q

When does the final expression of a for loop get evaluated?

A

each time after the code block runs

65
Q

Besides a return statement, which exits its entire function block, which keyword
exits a loop before its condition expression evaluates to false?

A

BREAK

66
Q

What does the ++ increment operator do?

A

adds and reassigns value

67
Q

How do you iterate through the keys of an object?

A

for in loop

68
Q

How do you serialize a data structure into a JSON string using JavaScript?

A

The JSON.stringify() method converts a JavaScript object or value to a JSON string, optionally replacing values if a replacer function is specified or optionally including only the specified properties if a replacer array is specified.

Web Development (9 decks)

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