Objects

Question 1

let user = new Object();

// the above is what type of object?

Answer 1

“object constructor” syntax

Question 2

let user = {};

// the above is what type of object?

Answer 2

“object literal” syntax

Question 3

an object has a property named?

Answer 3

key

Question 4

an objects key contains a ____?

Answer 4

value

Question 5

in a object a key can have multiple words but it must use ?

Answer 5

quoted

Question 6

multi word keys will not work with what and must use _____?

Answer 6

dot notation
brackets

Question 7

using bracket notation:
let user = {};

set a key “name” to “steve”

Answer 7

user[“name”]=”steve”;

Question 8

let user = {
names = “steve”
};

delete names using bracket notation.

Answer 8

delete user[‘names’];

Question 9

let user = {
names = “steve”
};

delete names using dot notation.

Answer 9

delete user.names

Question 10

let user = {
name: “John”,
age: 30
};
// print “30” using dot notation
// print “30” using brackets

Answer 10

console.log(user.age)
console.log(user[“age”]);

Question 11

write an object and add the number 5 to “bag” object

console.log(bag.apple);

Answer 11

let bag = {
[fruit]: 5,
};

Question 12

function makeUser(name, age) {
return {
name: name,
age: age,
};
}

How can the above be shortened and why?

Answer 12

function makeUser(name, age) {
return {
name,
age,
};
}

properties have the same names as variables

Question 13

let obj = {
for: 1,
let: 2,
return: 3
};

Will this give an error and why?

Answer 13

no

In short, there are no limitations on property names

Question 14

let obj = {
0: “test”
};

alert( obj[“0”] ); // returns

Answer 14

test

Question 15

let obj = {
0: “test”
};

alert( obj[0] ); // returns

Answer 15

test

Question 16

let user = {};
console.log( user.noSuchProperty === undefined );

// returns and why?

Answer 16

true

here will be no error if the property doesn’t exist!

Reading a non-existing property just returns undefined

Question 17

let user = { name: “John”, age: 30 };

alert( “age” in user ); //
alert( “blabla” in user ); //

Answer 17

true

false

Question 18

let obj = {
test: undefined
};

alert( obj.test ); // Returns?
alert( “test” in obj ); // Returns?

and why

Answer 18

undefined

true

In the code above, the property obj.test technically exists. So the in operator works right.

Question 19

for unknown or empty values we use _____

Answer 19

null

Question 20

let user = {
name: “John”,
age: 30,
isAdmin: true
};

// the below returns?
for (let key in user) {
alert( key );
}

Answer 20

name, age, isAdmin

Question 21

let user = {
name: “John”,
age: 30,
isAdmin: true
};

// the below returns?
for (let key in user) {
alert( user[key] );
}

Answer 21

John, 30, true

Question 22

let codes = {
“49”: “Germany”,
“41”: “Switzerland”,
“44”: “Great Britain”,
“1”: “USA”
};

for (let code in codes) {
alert(code);
}

// returns and why?

Answer 22

1, 41, 44, 49

integer properties are sorted, others appear in creation order.

Question 23

let user = {
name: “John”,
surname: “Smith”,
age: 25
};

for (let prop in user) {
alert( prop );
}
returns?

Answer 23

// name, surname, age

Question 24

let user = {
name: “John”,
surname: “Smith”,
age: 25
};

//write a for in loop so it shows name, surname and age

Answer 24

for (let prop in user) {
alert( prop );
}

Question 25

let user = {
name: “John”,
surname: “Smith”,
age: 25
};

write a for in loop so it shows
john, smith, 25

Answer 25

for (let prop in user) {
alert( user[prop] );
}

Question 26

let codes = {
“49”: “Germany”,
“41”: “Switzerland”,
“44”: “Great Britain”,
“1”: “USA”
};

for (let code in codes) {
alert(code); /
}

what to do write make this print 1, 41, 44, 49.

Answer 26

add + to all keys