While loops

Logging numbers

while loops will repeat a code block for as long as the condition is true.

js

let i = 1

while (i < 6) {
  console.log(i)
  i++ // increase i by 1 at the end of each loop
}

console.log('Done!')

output

1
2
3
4
5
Done!

TIP

The i++ is equivalent to i = i + 1 in javascript. It is very important as it guarantees the condition i < 6 eventually fails, avoiding an infinite loop.

Accumulating a value

Suppose we want to add all the odd numbers less than 100.

js

let n = 1
let total = 0 // we'll collect our answer here

while (n < 100) {
  total += n
  n += 2 // so n stays odd
}

console.log(total)

output

2500

Looping through an array

If we want to loop through an array, we can use the pointer i (or any other letter) to keep track of the index.

Perhaps we need to find the average rating of a list of books:

js

function average(arr) {
  let i = 0
  let total = 0

  while (i < arr.length) {
    total += arr[i]
    i++
  }

  return total / arr.length
}

const ratings = [4.25, 3.34, 2.6, 2.74, 2.36, 2.32, 3.94, 2.73]
console.log(average(ratings))

output

3.035