## Key Concepts

Review core concepts you need to learn to master this subject

### Reverse Loop

``````const items = ['apricot', 'banana', 'cherry'];

for (let i = items.length - 1; i >= 0; i -= 1) {
console.log(`\${i}. \${items[i]}`);
}

// Prints: 2. cherry
// Prints: 1. banana
// Prints: 0. apricot``````

A `for` loop can iterate “in reverse” by initializing the loop variable to the starting value, testing for when the variable hits the ending value, and decrementing (subtracting from) the loop variable at each iteration.

Loops
Lesson 1 of 1
1. 1
A loop is a programming tool that repeats a set of instructions until a specified condition, called a stopping condition is reached. As a programmer, you’ll find that you rely on loops all the …
2. 2
Before we write our own loops let’s take a moment to develop an appreciation for loops. The best way to do that is by showing you how cumbersome it would be if a repeated task required you to type …
3. 3
Instead of writing out the same code over and over, loops allow us to tell computers to repeat a given block of code on its own. One way to give computers these instructions is with a for loop. T…
4. 4
What if we want the for loop to log 3, 2, 1, and then 0? With simple modifications to the expressions, we can make our loop run backward! To run a backward for loop, we must: * Set the iterator va…
5. 5
for loops are very handy for iterating over data structures. For example, we can use a for loop to perform the same operation on each element on an array. Arrays hold lists of data, like customer n…
6. 6
When we have a loop running inside another loop, we call that a nested loop. One use for a nested for loop is to compare the elements in two arrays. For each round of the outer for loop, the inne…
7. 7
You’re doing great! We’re going to teach you about a different type of loop: the while loop. To start, let’s convert a for loop into a while loop: // A for loop that prints 1, 2, and 3 for (let cou…
8. 8
In some cases, you want a piece of code to run at least once and then loop based on a specific condition after its initial run. This is where the do…while statement comes in. A do…while statem…
9. 9
Imagine we’re looking to adopt a dog. We plan to go to the shelter every day for a year and then give up. But what if we meet our dream dog on day 65? We don’t want to keep going to the shelter for…
10. 10
Great job! In this lesson, we learned how to write cleaner code with loops. You now know: - Loops perform repetitive actions so we don’t have to code that process manually every time. - How to wri…

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