JavaScript - If Statements & Loops

1. If Statements & Boolean Operators

(1) If Statements

<!--If condition A is true, return B-->
if(A) {
	return B;
}

<!--IF condition A is true, return a.
If condition B is true, return B.
If neither one is true, return C.-->

if(A) {
	return a;
} else if (B) {
	return b;
} else {
	return c;
}

(2) Boolean Operators

Boolean operators are important for conditional code, 'cause it returns either true or false.

• ==: check for value equality
• !==: check for value inequality
• === and !==: check for value AND type (in)equality
• > and <: check for value being greater/smaller
• >= and <=: check for value being greater or equal
• !: check if NOT true

(3) The Logical AND and OR operators

AND and OR operators are meant to combine 2 or more conditions.

• &&(and): evaluated together(yields true if each condition yields true)
• ||(or): evaluated as an alternative

*Operator precedence

(4) ToBoolean Result

const nameInput = 'Nina'
if(nameInput) {
	...
}

This code works fine eventhough nameInput itself is not a condition. JS treis to coerce values to a boolean value if a boolean is required(it is a string which is not empty, so it returns true).

(5) Ternary Operator

const userName = isLogin ? 'Nina' : null

If isLogin(condition) is true, return 'Nina'. If not, return null.

(6) Switch-case Statement

<!--if statement-->
if(date === 1) {
console.log('Monday');
} else if(date ===2) {
console.log('Tuesday');
} else if(date ===3) {
console.log('Wednesday');
} else if(date ===4) {
console.log('Thursday');
} else if(date ===5) {
console.log('Friday');
} else if(date ===6) {
console.log('Saturday');
} else if(date ===7) {
console.log('Sunday');
}


<!--switch-case statement-->
Switch (date) {
case 1:
	console.log('Monday')
    	break;
case 2:
	console.log('Tuesday')
    	break;
case 3:
	console.log('Wednesday')
    	break;
case 4:
	console.log('Thursday')
    	break;
case 5:
	console.log('Friday')
    	break;
case 6:
	console.log('Saturday')
    	break;
case 7:
	console.log('Sunday')
    	break;
}

2. Loops

"Loops are handy, if you want to run the same code over and over again, each time with a different value."

(1) Kinds of Loops

for loop

'for loop' executes code a certain amount of times

	for(let i = 0; i < 3; i++){
	console.log(i);
	}

for-of loop

'for-of loop' executes for every element in an array

for(const el of array){
	console.log(el);
}

for-in loop

'for-in loop' executes for every key in an object

for(const key in obj){
console.log(key);
console.log(obj[key]);
}

while loop

'while loop' executes code as long as the condition is true

while(isLoggedIn){..}

while loop: checks the condition first
do-while loop: executes the condition first and then checks the condition

(2) Controlling Loop

Break

"The break statement can also be used to jump out of a loop.
The break statement breaks the loop and continues executing the code after the loop (if any):"

You can use "break" inside of the loop to stop the execution.

Continue

"The continue statement breaks one iteration (in the loop), if a specified condition occurs, and continues with the next iteration in the loop."

"continue" stops current execution, but doesn't stop the entire loop.