JavaScript basics loops
Tags: javascript, beginners
Published: 2021-08-28 05:07:35

In today's article on JavaScript basics, we'll be looking at different ways to create loops in JavaScript.

A loop is a way to iterate over code or execute code x times.

The different types of loops in JavaScript are:

- `for`
- `forEach`
- `for...in`
- `for...of`
- `while`
- `do...while`

## JavaScript for loop

I would say this is the godfather of loops. The basic for loop. Often you'll see this being used to loop over an array or execute code x times.

Let's first look at how we can create a loop that will execute five times.

```js
for (let i = 0; i < 5; i++) {
  // Execute 5 times
  console.log(`This is loop number ${i}`);
}

// This is loop number 0
// This is loop number 1
// This is loop number 2
// This is loop number 3
// This is loop number 4
```

However, often we want to loop over an array of items. Let's say we have some foods and want to loop each view.

```js
const foods = ['🍕', '🍗', '🍔', '🌮'];
for (let i = 0; i < foods.length; i++) {
  console.log(foods[i]);
}

// 🍕
// 🍗
// 🍔
// 🌮
```

## JavaScript forEach loop

Ever since ES6 came out, we were introduced to the forEach method, making looping arrays way easier!

```js
foods.forEach((item, index) => {
  console.log(`${index}: ${item}`);
});

// 0: 🍕
// 1: 🍗
// 2: 🍔
// 3: 🌮
```

Or as a one-liner:

```js
foods.forEach((item) => console.log(item));
```

## JavaScript for...in loop

Another cool thing we can do is loop through the properties of an object!

Let's say we want to loop each property of this user object.

```js
const user = {
  username: 'DailyDevTips',
  firstName: 'Chris',
  favoriteFood: '🍕',
};

for (let property in user) {
  console.log(`${property}: ${user[property]}`);
}

// username: DailyDevTips
// firstName: Chris
// favoriteFood: 🍕
```

## JavaScript for...of loop

Then we also have the `for...of` loop, which can iterate over specific values instead of the properties.

```js
const foods = ['🍕', '🍗', '🍔', '🌮'];
for (let value of foods) {
  console.log(value);
}
```

## JavaScript while loop

The next big thing in loops is the `while` loop. This means code is executed while a condition is not met.

For instance, let's say we have a boolean value, and we should execute code until it's true.

```js
let check = false;
while (!check) {
  console.log('not correct');
  check = true;
}
```

In this case, the code will execute once, be aware that this is a super-easy way to make an infinite loop that will crash your code!

With this, we can also evaluate a count, for instance, and only stop once the count is 5.

```js
let amount = 0;
while (amount < 5) {
  console.log(`amount ${amount}`);
  amount++;
}

// amount 0
// amount 1
// amount 2
// amount 3
// amount 4
```

## JavaScript do...while loop

The `do...while` is very similar to the while loop, but the executing order differs.

Let's first look at how it works:

```js
let test = true;
do {
  console.log('testing');
  test = false;
} while (test);

// testing
```

This will now execute once and evaluate that the test is not false.
However, what happens when we start with the test being false?

```js
let test = false;
do {
  console.log('testing');
  test = false;
} while (test);

// testing
```

Huh? This still logs testing. And yes it does
The `do...while` loop executes the code and THEN evaluates the while statement.
The `while` loop evaluates this code first before executing anything.

I hope you learned a thing or two about JavaScript loops!

I placed this code on a CodePen for you to check out and have a play around with.

{% codepen https://codepen.io/rebelchris/pen/xxdoVgY %}

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