# Why do we use loops?
To do repetitive tasks multiple times (automatically). Loop goes until condition gets false.
- break - interrupt loop.
- continue - skip item during iteration.
# Loops
for
while
do while
for of
forEach
for in# Interrupting & skipping Loops
break - interrupts a loop continue - skip certain iteration
// code stops, if 3 found in iteration
for (let i = 0; i <= 5; i++) {
if (i == 3) {
break
}
console.log(i)
}
// 0 1 2// 3 is skipped
for (let i = 0; i <= 5; i++) {
if (i == 3) {
continue
}
console.log(i)
}
// 0 1 2 4 5# Examples
# For Loop
when we know how many iterations we go.
let sum = 0
for (let i = 0; i < 101; i++) {
sum += i
}# While Loop
when we don’t specifically know how many iterations we go.
let count = prompt('Enter a positive number: ')
while (count > 0) {
console.log(count)
count--
}# Do-While Loop
runs at least once if condition is true/false.
let count = 11
do {
console.log(count)
count++
} while (count < 11)# For-of Loop
to iterate over an array/list … for every item.
const numbers = [1, 2, 3, 4, 5]
for (const number of numbers) {
console.log(number)
}# ForEach Loop
if we are interested in index of array. Can take 2 or 3 arguments: item, index, array.
const numbers = [1, 2, 3, 4, 5]
numbers.forEach((number, i) => {
console.log(number, i)
})
const countries = ['Finland', 'Sweden', 'Norway', 'Denmark', 'Iceland']
countries.forEach((country, i, arr) => {
console.log(i, country.toUpperCase())
})# For-in Loop
if we want to get object with specific key.
const user = {
firstName: 'Clemens',
lastName: 'Schmid',
age: 18,
country: 'Austria',
skills: ['HTML', 'CSS', 'JS', 'React'],
}
for (const key in user) {
console.log(key, user[key])
}