for loop iterating Array

let carsArray = ['BMW','Audi']
for (let i = 0; i < carsArray.length; i++) {
    console.log(carsArray[i]);
}

Output
BMW
Audi

for loop iterating Object

let carObject = {'name':'BMW','year':'2002'}
let carKeys = Object.keys(carObject);        //['name','year']
for (let i = 0; i < carKeys.length; i++) {
    console.log(carObject[carKeys[i]]);
}

Output
BMW
2002

forEach Example 1

let carsArray = ['BMW','Audi']
carsArray.forEach(e=> {
    console.log(e)
})

Output
BMW
Audi

forEach Example 2

let carsArray = ['BMW','Audi']
carsArray.forEach((e,index) => {
    console.log(e,'-',index)
})

Output
BMW - 0
Audi - 1

for in Array Example 1

for in looping give you access to the index in the array, not the actual element

let carsArray = ['BMW','Audi']
for (let i in carsArray) {
    console.log(i);
}

Output
0
1

for in Array Example 2

let carsArray = ['BMW','Audi']
for (let i in carsArray) {
    console.log(carsArray[i]);
}

Output
BMW
Audi

for in Object Example 1

let carObject = {'name':'BMW','year':'2002'}
for (let i in carObject) {
    console.log(i);
}

Output
name
year

for in Object Example 2

let carObject = {'name':'BMW','year':'2002'}
for (let i in carObject) {
    console.log(carObject[i]);
}

Output
BMW
2002

Nested for loop Example

let text = "";
for (let i = 0; i < 3; i++) {
  text += i + " ";   
  for (let j = 10; j < 13; j++) {
    text += j + " ";   
  }
console.log(text);
}

Output
0 10 11 12 
0 10 11 12 1 10 11 12 
0 10 11 12 1 10 11 12 2 10 11 12 

function Example 1

let number1 = 4, number2 = 3;
var x = myFunction(number1, number2);
console.log(x);

function myFunction(a, b) {
  return a * b;
}

Output
12

function Example 2

demo = "The temperature is " + toCelsius(77) + " Celsius";
console.log(demo)
function toCelsius(fahrenheit) {
  return (5/9) * (fahrenheit-32);
} 

Output
The temperature is 25 Celsius