Objects

Question 1

What are objects in JavaScript?

Answer 1

An object is data that contains key:value pairs

Question 2

How do we create objects in JavaScript

Answer 2

We create objects by containing the key:value pairs within curly braces. Multiple K:V need to be separated by commas

Question 3

How can we conceptualize the relationship between key and value in an object

Answer 3

Each key references a value

Much like a word and its definition in the dictionary

Question 4

What values can we put in an object?

Answer 4

Objects can contain any valid data structure - Primitives and Objects

Question 5

What is another name for keys in an JavaScript object?

Answer 5

Keys are also known as

Properties

Question 6

How can we get the value of an object property (key)?

Answer 6

We can use dot (.) operator (dot notation)

or

bracket [] notation

Question 7

Give the syntax for using dot notation to get the value of an object property.

Answer 7

objectName.propertyName

aka

objectName.keyName

Question 8

Give the syntax for using bracket notation to get the value of an object’s property

Answer 8

objectName[‘propertyName’]

note that the propertyName is a string

Question 9

When do you need to use bracket notation to access the value of an object’s properties?

Answer 9

1. When you access the value of a property with a variable.
2. When the property name is an invalid identifier

Question 10

How do we set the value of a property (key) in an object?

Answer 10

We can use either dot notation (preferred) or bracket notation

Question 11

Give the syntax for setting an object property value.

Answer 11

objectName.propertyName = value

we can use bracket notation too

Question 12

How do we delete an object key:value pair?

Answer 12

delete objectName.propertyName

we can use bracket notation too

Question 13

If two objects hold the same information will the equate to equal using comparison opperators?

Answer 13

No, objects are compared by reference, not by content.

Question 14

When will two variables that point to objects be equal using equality opperators?

Answer 14

Only when variables point to the same object, or one variable points to a variable pointing to an object, will they be equal.

Question 15

When do keys (or identifiers) need quotation marks in an object literal?

Answer 15

Then the key or identifier contains special characters (like a space).

Question 16

How do we create a method in an object literal?

Answer 16

Two ways:

1. Set the method name with the key, and the value as an anonymous function after the colon
2. Set the method name with the key, and create the function without the colon or function name

Question 17

Give the syntax for the ES6 method creation in an object.

Answer 17

const objectName = {

methodName () { method code block } }

Question 18

What does it mean that Objects are passed by reference

Answer 18

It means that when objects are assigned to variables, the variables hold a reference to the object’s location in memory, not that actual values. So, if we mutate a object by passing it to a function, the original object is mutated, regardless of the variable type.

Question 19

Can we reassign objects that are passed as a variable into a function?

Answer 19

No. Because objects are passed by reference, when we pass in a object variable to a function, the function variable references the location of data, but not the original variable. Any reassignment occurs only within the function body and not outside

Question 20

How can we iterate through objects?

Answer 20

The for … in loop with execute a given block of code for each property in an object

Question 21

Are key:value pairs in objects ordered?

Answer 21

No, key:value pairs are not ordered in objects.

Question 22

Do the methods of an object have direct access to other properties of that object.

Answer 22

Not directly, other properties are not contained within their scope.

You need to use the “this” keyword, which refers back to the calling object

Question 23

How do we use the keyword this in object methods?

Answer 23

We use the keyword this in object methods to gain access to the object properties outside the scope of the method’s code block. This will refer to the calling object, and we use dot-notation to select the property value we need.

Question 24

Will the keyword this work with methods written as arrow functions?

Answer 24

No, not without help. Arrow functions inherently bind their keyword this to the global object.

Question 25

Does JavaScript have built in privacy for objects?

Answer 25

No

Question 26

What is a conventional way of indicating that a property of an object is private in JavaScript?

Answer 26

We and prepend an underline “_” to the property name in an object to indicate privacy.

Question 27

What is the basic use-case for a getter method in JavaScript?

Answer 27

A getter method is basically used to get and return the value of an internal property of an object.

Question 28

What is the syntax of a getter method in JavaScript?

Answer 28

object {

get fullName() {

codeBlock

}}

Question 29

How do we call or invoke a getter method in JavaScript?

Answer 29

We invoke a getter method much like we would access a regular property value of an object.

object.getterName

We do not use the get keyword or add ( ) to the call.

Question 30

What are four advantages to using getter methods on objects?

Answer 30

1. We can use the keyword this to access object properties
2. We can manipulate or formate properties within the method
3. We can use conditionals to return different values
4. The code is easier to read and clearer

Question 31

What should we keep in mind when naming properties and getter methods?

Answer 31

Getter methods and object properties may not share names.

Question 32

What do setters do in the context of JavaScript objects?

Answer 32

Setters reassign the value of an object property

Question 33

Describe the syntax of a setter method in a JavaScript object

Answer 33

objectName {

set age (newAge){

if(typeof newAge === ‘number’){

this._age = newAge

} else {

return ‘age must be a number

}}}

Question 34

How do we invoke a setter method?

Answer 34

objectName.setterName = value

We do not use ( ) when invoking the setter

Question 35

What is a factory function?

Answer 35

A factory function is a function used to create objects from a basic design or schema.

Instead of creating multiple object literals, we can use the factory function to create objects

Question 36

What is the syntax of a factory function.

Answer 36

const factoryName = (property1, property2, property3) => {

return {

property1: property1,
property2: property2,
property3: property3,

aMethod() {

methodCode}

}

}

Question 37

What is ‘property value shorthand’ in relation to JavaScript objects?

Answer 37

Property Value Shorthand is a type of destructuring available in ES6.

Question 38

How do we use property value shorthand to assign values to properties in JavaScript objects?

Answer 38

When the property and value share their name (as in factory functions) we can list only the property name and omit the value (since it is the same).

Question 39

Convert this factory function into property value shorthand:

function robotFactory(model, mobile){

return {

model: model,
mobile: mobile,

beep() {

console.log(‘Beep Boop’);

}

Answer 39

function robotFactory(model, mobile){

return {

model,

mobile,

beep() {

console.log(‘Beep Boop’);

}

Question 40

What is a ‘destructured assignment” in relation to JavaScript objects?

Answer 40

A destructure assignment is a shorthand method to assign property values to a variable.

Question 41

Give the syntax of a destructured assignment.

Answer 41

const {propertyName } = object

const will now equal propertyValue of propertyName

We still refer to the const by the propertyName

Question 42

What are Object class methods?

Answer 42

Object class methods are methods “built-in” to the Object prototype that we can call on the Object data-type.

Question 43

What are two or three common Object Class Methods that we might use?

Answer 43

Object.entries(objectName) = returns an array of key:value pairs

Object.keys(objectName) = returns an array of properties

Object.values(objectName) = returns an array of values of an objects properties

Question 44

What is unusual about the invocation of a setter method?

Answer 44

When using a setter method we do not include the arguments in parenthesis - instead, we set the objectName.setterMethod = arguments