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Terry Threatt
Terry Threatt

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How I learned Javascript Loops

In life we understand Loops to be a repetitive direction an object is traveling in perpetuity or until some condition forces the looping to stop.

Computers are actually quite well-suited to do repetitive tasks like looping and running sub-task during each iteration of the loop. So virtually every programming has a concept of looping built-in but may actually look a bit different in implementation and execution.

Javascript Loops

In Javascript, my current language of choice a loop can look like this.

for(let i = 0; i < array1.length; i++){

It can also make use of control statements like break or continue to control the flow of the loop.

break: This will break out of the loop on command

continue: This will continue the loop on command

Here are the four basic parts of a loop:

  • Initialization: ex: let i = 0

This will serve as a counter for each element in the array.

Click here to learn more about arrays

  • Condition: ex: i < array1.length

This condition is checked at each iteration of the loop and continues to a sub-task for each element unless the condition is false, A false condition will immediately stop the loop and produce a return value if given.

Here we are using the length of an array to check if each iteration is less than the array length with the array1.length method.

  • Final-Expression: ex: i++

The final expression is generally an instruction to decrement or increment the initialized value until we meet our condition that causes the end of the loop.

  • Statement: ex: console.log(array1[i])

The statement will consist of any sub-tasks you want to do with each element in the array. In this case, we are logging each element of the array to the console efficiently with the loop.


Here are the different types of loops in Javascript:

for loop

const numbers = [ 2, 3, 7, 11]
let sum = 0

for (let i = 0; i < numbers.length; i++){
    sum += numbers[i]
    console.log(sum, i) 

// => output: 
2 0
5 1
12 2
23 3 
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while loop

const numbers = [ 2, 3, 7, 11]

let i = 0 // initialization happens here 

while(i < 4){ // condition happens here 
   console.log(numbers[i], i)
   i++ // final-expression happens here

// => output: 
2 0
3 1
7 2
11 3 
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do..while loop

const numbers = [ 2, 3, 7, 11]
let i = 0

do {
  if (numbers[i] % 2 === 0) {
    console.log(numbers[i] + ' is even') 
  } else {
    console.log(numbers[i] + ' is odd')
} while (i < numbers.length)

// => output:
2 is even
3 is odd
7 is odd
11 is odd
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Bonus: Also try to give these for..of & loops a spin.

Let's chat about Loops

Hopefully, this helped you to learn a bit about loops or bring my understanding about how they work. If you enjoyed this post feel free to leave a comment about your thoughts and experiences working with loops in Javascript.

Happy Coding,
Terry Threatt

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