Loops and Iteration

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What Are Loops in JavaScript?

Loops and Iteration What Are Loops in JavaScript?

Learning Goal

Understand what loops are, why they’re used in programming, and how they help you write cleaner, smarter code.

Concept: Repeating Code Efficiently

In JavaScript (and most programming languages), loops allow you to repeat a block of code multiple times without having to write it again and again.

Without a loop:

Let’s say you want to print “Hello!” 5 times:

console.log("Hello!");
console.log("Hello!");
console.log("Hello!");
console.log("Hello!");
console.log("Hello!");

This works, but it’s:

  • Long
  • Repetitive
  • Hard to update (what if you want 100 lines?)

With a loop:

for (let i = 0; i < 5; i++) {
  console.log("Hello!");
}

This prints “Hello!” 5 times — but the code is:

  • Shorter
  • Easier to read
  • Easy to update (just change 5 to any number)

What Exactly Is a Loop?

A loop is a programming tool that:

  • Starts at a specific value (like 0)
  • Checks a condition (e.g., is i < 5?)
  • Executes a block of code if the condition is true
  • Repeats the process until the condition becomes false

Visual Example:

StepWhat Happens
i = 0Check: Is i < 5? → Yes → Run code
i = 1Check: Is i < 5? → Yes → Run code
i = 2Yes → Run code
i = 3Yes → Run code
i = 4Yes → Run code
i = 5No → Stop the loop

Real-Life Analogy

Doing Push-Ups at the Gym

You want to do 10 push-ups. Instead of:

  • “Do 1 push-up”
  • “Do 1 push-up”
  • …

You say:

“Repeat push-up 10 times”

That’s what a loop does in code.

Why Are Loops Useful?

Loops are powerful because they let you:

Use CaseExample
Repeat a taskDisplay a message multiple times
Process a listGo through all items in an array
Automate behaviorAnimate something on a website
Search dataFind a value inside a dataset
Validate inputCheck every field in a form

Simple Loop Example in JavaScript

for (let i = 1; i <= 3; i++) {
  console.log("This is loop number " + i);
}

Output:

This is loop number 1
This is loop number 2
This is loop number 3

Key Takeaways

  • Loops repeat code automatically
  • Save time and make code more efficient
  • Work by setting a start, checking a condition, and repeating until it’s no longer true
  • There are several types of loops (e.g., for, while, do...while) that we’ll explore next
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