abc-notepedia

# Operators

# Mathematical operators

Mathematical operators
+ Addition (and also used for concatenating strings) -> can cause errors, if an element is a string
- Subtraction
/ Division
% Modulus (Division Remainder)
++ increment. counter++ is the same as: counter = counter + 1
-- decrement
** Exponentiation (same (but newer) as : Math.pow())

# Assignment Operators

Assignment Operators
= assigns a value
+= x += is the same as x= x + y
-= x -= is the same as x= x - y
*= x *= is the same as x= x * y
/= x /= is the same as x= x / y
%= x %= is the same as x= x % y
**= x **= is the same as x= x ** y

# Comparison Operators

result is always: true=1, false=0

Comparison Operators
== equal to
!= not equal
< less than
> greater than
<= less than or equal to
>= greater than or equal to
=== equal value and equal type - strict equality (usually preferred)-> additional Information (opens new window)
!== not equal value and equal type
let res = 5 == 2 + 3;
console.log(res);

Comparing an object: checks, if they point to the same object in memory

# Truthy & Falsy

Theese values evaluate to false when checked as a condition (falsy):

  • 0
  • Empty strings like "" or ''
  • null which represent when there is no value at all
  • undefined which represent when a declared variable lacks a value
  • NaN, or Not a Number

this is often used to check, if an object exsits.

Difference when using comparison opreators:

Truthy & Falsy
(false == 0) (false === 0) true false
(false == '') (false === '') true false
(0 == '') (0 === '') true false
(undefined == 0) (undefined === 0) true false
NaN == Nan false. NaN is a non defineable Number. 2 NaN can not be equal

# Logical Operators

&& logical AND (both sides need to be true)
|| logical OR (one side needs to be true)
! logical NOT (turns true to false and vice versa)

The ! not operator reverses, or negates, the value of a boolean:

let excited = true;
console.log(!excited); // Prints false

# Typeof Operator

Check the data types of the variables -> returns a string of the data type.

Syntax: typeof is a global operator so can be called on any object, .length is an object attribute and can only be called in the context of an existing object instance.

const unknown1 = 'foo';
console.log(typeof unknown1); // Output: string

const unknown2 = 10;
console.log(typeof unknown2); // Output: number

const unknown3 = true; 
console.log(typeof unknown3); // Output: boolean

← Numbers →