JavaScript

Question 1

Name all the truthy values in javascript.

Answer 1

• {}
• []
• 42
• “false”
• new Date(),
• -42
• 3.14
• -3.14
• Infinity
• -Infinity
• all objects

Question 2

Name all the falsy values in javascript.

Answer 2

• false (boolean)
• 0
• -0
• 0n
• ””
• null
• undefined
• NaN

Question 3

in a method, what does this refer to?

Answer 3

the owner object

Question 4

in strict mode, what does this refer to?

Answer 4

undefined

Question 5

What’s an expression in Javascript?

Answer 5

any line of code that resolves to a value.
(can still resolve to null or undefined)

Question 6

What’s a statement in Javascript?

Answer 6

performs an action. Doesn’t necessarily return a value.

Question 7

What is Object restructuring ?

Answer 7

allows you to extract properties from an object into individual variables

Question 8

What does a Spread operator do?

Answer 8

allows an iterable such as an array or string to be expanded in places where zero or more arguments or elements are expected.

Question 9

Describe strict mode.

Answer 9

Helps eliminate some silent errors by changing them into throw errors

In strict mode, this is undefined in functions that are not methods or constructors.

Question 10

What is the global object?

Answer 10

the default container that holds functions, variables and built in objects ( Math, Date, console etc.)

Question 11

What is the owner object?

Answer 11

the object the method belongs to.

Question 12

Are functions objects?

Answer 12

Yes.

Question 13

In an array what does push() do?

Answer 13

add new elements(multiple) to the end of array + returns it.

Question 14

In an array what does pop() do?

Answer 14

Removes the last element (one at a time) from an array, and returns it.

Question 15

In an array what does shift() do?

Answer 15

Removes the first element from an array, and returns that. (one at a time)

Question 16

In an array what does unshift() do?

Answer 16

Adds new elements to the beginning of an array, and returns
the new length.

Question 17

In an array what does slice() do?

Answer 17

Returns a shallow copy of a portion of an array.

Question 18

In an array what does splice() do?

Answer 18

Changes the contents of an array by removing or replacing
existing elements and/or adding new elements.

Question 19

In an array what does concat() do?

Answer 19

Used to merge two or more arrays, and returns a new array.

Question 20

What is an object?

Answer 20

A JavaScript object is a collection of properties where each property is an association between a key and a value.

Question 21

What is an object literal?

Answer 21

a list of zero or more pairs of property names and
associated values of an object, enclosed in curly braces ({}).

Question 22

What’s the first line of an object constructor?

Answer 22

let object_name = new Object();

Question 23

What does Object.keys() do?

Answer 23

returns an array of all the object’s keys.

Question 24

What does Object.entries() do?

Answer 24

returns an array of all the object’s key/value pairs

aka all keys and all values.

Question 25

What does `Object.assign()` do?

Answer 25

copy original object’s properties to new `copy_object,` returns `copy_object.`

Question 26

What does the rest parameter do?

Answer 26

allows a function to accept any number of arguments as an array.