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Learning Fuze Full Stack > Javascript > Flashcards

Javascript Flashcards

1
Q

What is the purpose of variables?

A

To store data.

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2
Q

How do you declare a variable?

A

keyword(var, let, const) with a space followed by the variable number.

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3
Q

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

A

Using the assignment operator ‘=’

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4
Q

What characters are allowed in variable names?

A

start with $ _ or letters, and can have numbers and letters in it.

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5
Q

What does it mean to say that variable names are “case sensitive”?

A

javascript reads capitals as a differnet letters.

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6
Q

What is the purpose of a string?

A

To store text data.

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7
Q

What is the purpose of a number?

A

To store numbers for use in math.

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8
Q

What is the purpose of a boolean?

A

As a ‘on, off’ switch.

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9
Q

What does the = operator mean in JavaScript?

A

It assigns the value to a variable.

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10
Q

How do you update the value of a variable?

A

using a the variable name and assignment operator.

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11
Q

What is the difference between null and undefined?

A

undefined means the variable has not been assigned a variable. Null is purposefully left unassigned.

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12
Q

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

A

To keep things organized and to know what and why your logging something.

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13
Q

Give five examples of JavaScript primitives.

A

boolean, number, string, null, undefined.

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14
Q

What data type is returned by an arithmetic operation?

A

A number

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15
Q

What is string concatenation?

A

Combining strings togethers.

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16
Q

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

A

Add two values to another.

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17
Q

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

A

A boolean value.

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18
Q

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

A

It adds or concatenates two numbers or strings and then assigns to the variable.

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19
Q

What are objects used for?

A

Used to group together sets of variables and function(methods).

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20
Q

What are object properties?

A

They are variables describing the variable they are in.

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21
Q

Describe object literal notation.

A

variable assign with {} and key value property pairs.

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22
Q

How do you remove a property from an object?

A

use the delete keyword and the property of the object.

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23
Q

What are the two ways to get or update the value of a property?

A

using dot or bracket notation and assignment operator.

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24
Q

What are arrays used for?

A

Relevant data or lists of data.

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25
Q

Describe array literal notation.

A

var array = []

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26
Q

How are arrays different from “plain” objects?

A

arrays properties are the index

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27
Q

What number represents the first index of an array?

A

The index starts at 0.

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28
Q

What is the length property of an array?

A

the .length property shows the number of items.

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29
Q

How do you calculate the last index of an array?

A

item.length -1 will give the last index since index starts at 0.

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30
Q

What is a function in JavaScript?

A

Is a special object that can be called to run a block of code.

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31
Q

Describe the parts of a function definition.

A

function keyword, optional name and optional paramaters and the code block.

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32
Q

Describe the parts of a function call.

A

function name and optional arguments in ().

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33
Q

When comparing them side-by-side, what are the differences between a function call and a function definition?

A

function call uses parameters instead of arguments, and does not have the function definition and no code block.

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34
Q

What is the difference between a parameter and an argument?

A

parameter is an empty variable or placeholder and arguments are values passed through.

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35
Q

Why are function parameters useful?

A

They allow use to create lines of code to run with the parameters, arguments when you call the function.

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36
Q

What two effects does a return statement have on the behavior of a function?

A

It produces a usable value and exits the function.

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37
Q

Why do we log things to the console?

A

We log to the console to see if our output is what we expected.

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38
Q

What is a method?

A

A method is a function of an object.

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39
Q

How is a method different from any other function?

A

The method must be called in relation to a object, (arrays and strings are objects?)

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40
Q

How do you remove the last element from an array?

A

this.pop() removes the last items from an array AND returns it, so it may be assigned to a variable.

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41
Q

How do you round a number down to the nearest integer?

A

your use the floor() method of the Math object. Math.floor() and pass the number as an argument.

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42
Q

How do you delete an element from an array?

A

You can use the array.splice() method, with arguments in order.
(start index, number to delete, items to replace, items to replace..), also
array.shift, and array.pop

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43
Q

How do you append an element to an array?

A

You can use array.push to put an item at the end of an array or array.unshift to place it at the beginning.

44
Q

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

A

They only change a string locally and return the value leaving the original string variable the same.

45
Q

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

A

about 50.

46
Q

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

A

Not always sometimes you don’t need the returned value.

47
Q

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

A

40 - 50

48
Q

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

A

MDN

49
Q

How do you generate a random number?

A

Math.Random

50
Q

How do you break a string up into an array?

A

string.split

51
Q

Give 6 examples of comparison operators.

A

<, >, <=, >=, ===, !==, &&, ||

52
Q

What data type do comparison expressions evaluate to?

A

Booleans

53
Q

What is the purpose of an if statement?

A

To run code if a condition is met.

54
Q

Is else required in order to use an if statement?

A

The else is not required, but is good for formatting.

55
Q

Describe the syntax (structure) of an if statement.

A

if (condition) {code block}

56
Q

What are the three logical operators?

A

&&, ||, !

57
Q

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

A

With && and ||.

58
Q

What is the purpose of a loop?

A

to run a code block a certain amount of times under a condition.

59
Q

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

A

Tells us when to stop the loops.

60
Q

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

A

Every time a code block is run a new time.

61
Q

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

A

at the beginning of each iteration.

62
Q

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

A

At the beginning of each iteration.

63
Q

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

A

after the intialization.

64
Q

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

A

after the code block is run.

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

It increases a variable by 1

67
Q

How do you iterate through the keys of an object?

A

With a for…in loops.

68
Q

What is JSON?

A

data storage in string format for easy transfer and storage of data models

69
Q

What are serialization and deserialization?

A

serialization is turning objects or array into jsons string format; and desrialization is the reverse, taking the string format and converting it into a javascript object or array

70
Q

Why are serialization and deserialization useful?

A

data can be sent and stored outside of javascript.

71
Q

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

A

JSON.stringify()

72
Q

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

A

JSON.parse()

73
Q

How do you store data in localStorage?

A

Using the method setItem of the localStorage object and pass through prefferably your JSON data.

74
Q

How do you retrieve data from localStorage?

A

Using the method getItems() of the localStorage object.

75
Q

What data type can localStorage save in the browser?

A

A key value pair. of strings

76
Q

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

A

before the page closes.

77
Q

What is a method?

A

method is a function of an object.

78
Q

How can you tell the difference between a method definition and a method call?

A

object.method() to call
definitions
object.method : function () {}

79
Q

Describe method definition syntax (structure).

A

a property of an object, with colon and then function keyword and normal building of an anonymous function.

80
Q

Describe method call syntax (structure).

A

object.method()

81
Q

How is a method different from any other function?

A

It is called with an object.

82
Q

What is the defining characteristic of Object-Oriented Programming?

A

objects can contain both data as properties and functions as methods

83
Q

What are the four “principles” of Object-Oriented Programming?

A

Abstraction, Encapsulation, Inheritance, Polymorphism

84
Q

What is “abstraction”?

A

A simple way of interacting with something. Without understanding the complicated way it happens.

85
Q

What does API stand for?

A

Application programming interface

86
Q

What is the purpose of an API?

A

Allows us to interface with a database in a simple manner.

87
Q

What is this in JavaScript?

A

this is a reference of an object, if no object then the window.

88
Q

What does it mean to say that this is an “implicit parameter”?

A

a parameter that is available to use even though it has not been defined. A reference of an object

89
Q

When is the value of this determined in a function; call time or definition time?

A

this value is determined at call time.

90
Q

What does this refer to in the following code snippet?
var character = {
firstName: ‘Mario’,
greet: function () {
var message = ‘It's-a-me, ‘ + this.firstName + ‘!’;
console.log(message);
}
};

A

this refers to the window till its called.

91
Q

Given the above character object, what is the result of the following code snippet? Why?
character.greet();

A

It’s me mario, because this of greet will reference character.

92
Q

Given the above character object, what is the result of the following code snippet? Why?
var hello = character.greet;
hello();

A

the result of this will be undefined.

93
Q

How can you tell what the value of this will be for a particular function or method definition?

A

You cannot.

94
Q

How can you tell what the value of this is for a particular function or method call?

A

look to the left of the ‘.’ or else it is default window.

95
Q

What kind of inheritance does the JavaScript programming language use?

A

Prototypal Inheritance

96
Q

What is a prototype in JavaScript?

A

The ancestor of data.

97
Q

How is it possible to call methods on strings, arrays, and numbers even though those methods don’t actually exist on strings, arrays, and numbers?

A

They are special objects?

98
Q

If an object does not have it’s own property or method by a given key, where does JavaScript look for it?

A

In its prototype tree.

99
Q

What does the new operator do?

A

1.Creates a Blank Object.
2. references the constructor as a prototype.
3.runs the constructor function.
4.An extra step to see if something other than an object was created.

100
Q

What property of JavaScript functions can store shared behavior for instances created with new?

A

Their prototype.

101
Q

What does the instanceof operator do?

A

Checks if a constructor function matches an object.

102
Q

What is a “callback” function?

A

A function that is called as an arguement.

103
Q

Besides adding an event listener callback function to an element or the document, what is one way to delay the execution of a JavaScript function until some point in the future?

A

setTimeout() method.

104
Q

How can you set up a function to be called repeatedly without using a loop?

A

using setInterval() method

105
Q

What is the default time delay if you omit the delay parameter from setTimeout() or setInterval()?

A

0, run immediately.

106
Q

What do setTimeout() and setInterval() return?

A

an ID number for their timer

Learning Fuze Full Stack (6 decks)

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