Types in JS

Question 1

Null

Answer 1

Absence of value

Question 2

Undefined

Answer 2

absence of definition

Question 3

What are the 7 JS falsy values?

Answer 3

1. false
2. null
3. undefined
4. 0
5. NaN
6. ””
7. document.all

Question 4

What are primitive types?

Answer 4

Values can contain only a single thing (versus Objects, non-primitive) that are used to store collections of data and more complex entities.

It is immutable, can’t be broken down further.

Question 5

What are the 7 basic types in JS?

Answer 5

1. number for numbers of any kind: integer or floating-point.
2. string for strings. A string may have one or more characters, there’s no separate single-character type.
3. boolean for true/false.
4. null for unknown values – a standalone type that has a single value null.
5. undefined for unassigned values – a standalone type that has a single value undefined.
6. object for more complex data structures.
7. symbol for unique identifiers.

Question 6

Explain how objects are stored and copies “by reference”

Answer 6

A variable stores not the object itself, but its “address in memory”, in other words “a reference” to it.

When an object variable is copies – the reference is copied, the object is not duplicated.

Passing by reference saves space in memory.

https://javascript.info/object

Question 7

What is the difference between == and ===?

Answer 7

== is the abstract equality operator while === is the strict equality operator. The == operator will compare for equality after doing any necessary type conversions. The === operator will not do type conversion, so if two values are not the same type === will simply return false. When using ==, funky things can happen, such as:

1 == '1'; // true
1 == [1]; // true
1 == true; // true
0 == ''; // true
0 == '0'; // true
0 == false; // true