JAVASCRIPT

JavaScript Code Block: Syntax, Usage, and Examples

A JavaScript code block is a group of one or more statements enclosed in curly braces {}. Code blocks are used to control which pieces of code run and when, especially inside conditionals, loops, and functions.

How to Use a Code Block in JavaScript

To write a code block in JavaScript, simply wrap your statements inside {}. This structure groups the code together and tells JavaScript to treat it as one unit.

if (true) {
  console.log("I'm inside a code block!");
}

The curly braces here define the code block. Even if there's only one statement inside, using {} clearly marks the beginning and end of that block.

You’ll see code blocks in JavaScript used in many places:

  • After if, else if, and else
  • In for, while, and do...while loops
  • Inside functions
  • Inside arrow functions with multiple statements

When to Use JavaScript Code Blocks

Code blocks aren't just decorative — they're essential for grouping logic and defining scope. Here are some common scenarios where you'll use a code block in JavaScript.

1. Conditional Logic

A code block is required if you want to execute multiple statements in an if or else block. Without curly braces, only the next line runs.

const age = 20;

if (age >= 18) {
  console.log("You can vote.");
  console.log("And get a driver's license.");
}

2. Loops

Every loop structure in JavaScript relies on a code block to know which code should repeat.

for (let i = 0; i < 3; i++) {
  console.log("Loop number:", i);
}

3. Function Bodies

Functions must have a block to contain their code. Even a short function like this one uses a code block.

function greet() {
  console.log("Hello!");
}

4. Arrow Functions with Multiple Lines

For arrow functions, a code block is required if you're doing more than just returning a value.

const sayHi = () => {
  const name = "Tariq";
  console.log(`Hi, ${name}!`);
};

Examples of JavaScript Code Blocks

Let’s look at different types of code blocks in action.

Example 1: Code Block in an If Statement

const isRaining = true;

if (isRaining) {
  console.log("Take an umbrella.");
  console.log("Or wear a raincoat.");
}

Without the code block, only the first line would run. The second would run regardless of the condition.

Example 2: Code Block in a Loop

let count = 0;

while (count < 2) {
  console.log("Counting:", count);
  count++;
}

The code block includes both console.log and count++, so both happen with each loop.

Example 3: Code Block in a Function

function sum(a, b) {
  const result = a + b;
  return result;
}

Here, the code block groups the variable declaration and the return statement.

Example 4: Code Block in an Else Block

const isLoggedIn = false;

if (isLoggedIn) {
  console.log("Welcome back!");
} else {
  console.log("Please log in.");
}

The else block runs only if the if condition fails. The {} ensure the right group of actions runs.

Learn More About JavaScript Code Blocks

Code Block Scope

Each JavaScript code block introduces a new block scope. This affects how variables behave. For example, let and const variables are only accessible inside the block where they’re declared.

{
  let secret = "hidden";
  console.log(secret); // works
}
console.log(secret); // ReferenceError

This concept helps prevent bugs and keeps your variables tidy.

Code Blocks vs. Single-Line Statements

JavaScript allows single-line statements without code blocks, but this can lead to problems.

if (true)
  console.log("Only this runs");
  console.log("This always runs"); // ⚠️ Runs regardless of the condition

Adding a code block avoids confusion:

if (true) {
  console.log("Now it's clear both belong to the if!");
}

Nested Code Blocks

You can place one code block inside another. This is common in nested conditionals or loops.

for (let i = 0; i < 2; i++) {
  if (i === 1) {
    console.log("Nested block triggered");
  }
}

Nested blocks help organize complex logic and keep related actions grouped together.

Formatting and Readability

Using code blocks consistently improves readability. Even when JavaScript doesn't require them, it's a good habit to include {} — especially when you're working on a team or revisiting your own code later.

Learn JavaScript for Free
Start learning now
button icon
To advance beyond this tutorial and learn JavaScript by doing, try the interactive experience of Mimo. Whether you're starting from scratch or brushing up your coding skills, Mimo helps you take your coding journey above and beyond.

Sign up or download Mimo from the App Store or Google Play to enhance your programming skills and prepare for a career in tech.

You can code, too.

© 2025 Mimo GmbH