reading-notes

Operators and Loops in JavaScript

Expressions & Operators - Web Docs

Loops & Iteration

Arithmetic Operators

Operator	Description
+	Addition
-	Subtraction
*	Multiplication
**	Exponential
/	Division
%	Modulus (Division Remainder)
++	Increment
–	Decrement

Assignment Operators

Operator	Example	Same As
=	x = y	x = y
+=	x += y	x = x + y
-=	x -= y	x = x - y
*=	x *= y	x = x * y
/= x	/= y	x = x / y
%=	x %= y	x = x % y
**= x	**= y	x = x ** y

Adding JS Strings

• The + operator can also be used to concatenate strings
• This also applies adding numbers and strings together, however, the final output will be a string, NOT a number

let text1 = "John";
let text2 = "Doe";
let text3 = text1 + " " + text2;

// output of text3 = 'John Doe'

Comparison Operators

Operator	Description
==	equal to
===	equal value and equal type
!=	not equal
!==	not equal value or not equal type
>	greater than
<	less than
>=	greater than or equal to
<=	less than or equal to
?	ternary operator

Logical Operators

Operator	Description
&&	logical and
||	logical or
!	logical not

Type Operators

Operator	Description
typeof	Returns the type of a variable
instanceof	Returns true if an object is an instance of an object type

Bitwise Operators

• Bit operators work on 32 bits numbers
• Any numeric operand in the operation is converted into a 32 bit number and the result is converted back to a JS number

Operator	Description	Example	Same As	Result	Decimal
&	AND	5 & 1	0101 & 0001	0001	1
|	OR	5 | 1	0101 | 0001	0101	5
~	NOT	~ 5	~0101	1010	10
^	XOR	5 ^ 1	0101 ^ 0001	0100	4
«	left shift	5 « 1	0101 « 1	1010	10
»	right shift	5 » 1	0101 » 1	0010	2
»>	unsigned right shift	5 »> 1	0101 »> 1	0010	2

Loops and Iteration

• Loops allow you to execute a piece of code to do something repeatedly given a set of conditions
• Types of Loops
  • Do
  • For
  • While

For Statement

• A for loop repeats until a specified condition evaluates to false

Syntax:

for ([initialExpression]; [conditionExpression]; [incrementExpression])
  statement

Example:

let countDown = 10 // Set initial condition in variable
for (let i = countDown; i >= 0; i--) // While i >= 0, decrement by 1, then exit the loop
  {
    console.log(`${i} second${i !== 1 ? 's' : ''} until lift off!`) // Logs count of i
   }
console.log('Lift Off!') // When i < 0, log 'Lift Off!'

Do…While Statement

• The do...while statement repeats until a specified condition evaluates to false

Syntax:

do
  statement
while (condition);

Example:

let i = 0; // Set initial condition
do {  // Do the statement below
  i += 1;
  console.log(i);
} while (i < 5); // While i is < 5

While Statement

• A while statement executes its statements as long as a specified condition is true
• If the condition becomes false, statement within the loop stops executing and control passes to the statement that follows the loop
  • NOTE: The condition test occurs before statement is the loop is executed
    • If the condition is true the loop continues, if false, the loop ends and the program moves on to the next block of code

Syntax:

while (condition)
  statement

Example:

let i = 10
while (i >= 0){ // While i is >= 0, the statement will execute
  console.log(`Countdown: ${i}`) // First log value of i
  i-- // Then decrement i by 1
}
console.log('Blast off!') // When i drops below 0, log 'Blast Off'