JavaScript Conditions: Syntax, Usage, and Examples

Conditions in JavaScript let your code make decisions. They evaluate to either true or false and are the core of control flow in any program.

How to Use Conditions in JavaScript

Conditions are used inside control statements like if, else, else if, switch, and loops. They go inside parentheses and evaluate a boolean expression.

if (temperature > 30) {
  console.log("It's hot outside.");
}

In this example, the code runs only if the condition (temperature > 30) is true. If the condition is false, JavaScript skips the code block.

You can also use multiple conditions with logical operators:

if (isSunny && temperature > 20) {
  console.log("Perfect day for a picnic.");
}

When to Use Conditions in JavaScript

Conditions help you control how your program behaves. You’ll use them anytime you want different outcomes depending on data, user actions, or system state.

1. Handling User Input

Conditions can validate input or control what feedback to give based on the user's choices.

let age = 17;
if (age >= 18) {
  console.log("You can vote.");
} else {
  console.log("You must be 18 or older.");
}

2. Managing Application States

They’re helpful for managing app states, such as toggling a feature, checking if a user is logged in, or hiding/showing UI elements.

if (userLoggedIn) {
  showDashboard();
} else {
  redirectToLogin();
}

3. Running Code Based on Environment

Conditions also help in determining how your app runs depending on the environment.

if (process.env.NODE_ENV === "production") {
  console.log("Running in production mode");
} else {
  console.log("Development mode enabled");
}

Examples of JavaScript Conditions

Here are three practical examples that show how to use conditions in JavaScript.

Example 1: Simple Boolean Check

let isOnline = true;

if (isOnline) {
  console.log("User is online");
} else {
  console.log("User is offline");
}

This uses a basic condition to check if a variable is true or false.

Example 2: Comparing Values

let score = 85;

if (score >= 90) {
  console.log("Grade: A");
} else if (score >= 80) {
  console.log("Grade: B");
} else {
  console.log("Keep practicing!");
}

This shows a common use of multiple conditions using else if.

Example 3: Nested Conditions

let isMember = true;
let hasCoupon = false;

if (isMember) {
  if (hasCoupon) {
    console.log("You get 30% off!");
  } else {
    console.log("You get 10% off!");
  }
} else {
  console.log("Sign up to save!");
}

Nested conditions allow for more complex decision-making.

Learn More About JavaScript Conditions

Truthy and Falsy Values

In JavaScript, conditions aren’t just about true or false. Many values evaluate as truthy or falsy:

Falsy values include:

• false
• 0
• "" (empty string)
• null
• undefined
• NaN

Everything else is considered truthy, even things like '0' or {}.

let value = "";

if (value) {
  console.log("This is truthy");
} else {
  console.log("This is falsy"); // This will run
}

Logical Operators in Conditions

You can combine conditions using logical operators:

• && (AND) – All conditions must be true.
• || (OR) – At least one condition must be true.
• ! (NOT) – Reverses the truthiness.

let age = 25;
let hasTicket = true;

if (age >= 18 && hasTicket) {
  console.log("You can enter.");
}

The Ternary Operator

The ternary operator lets you write shorter conditional statements:

let age = 16;
let message = age >= 18 ? "Welcome!" : "Come back later.";
console.log(message);

It’s handy for simple if/else checks on one line.

Switch Statements

When you have many values to compare, switch statements can be cleaner than multiple if/else blocks.

let fruit = "apple";

switch (fruit) {
  case "apple":
    console.log("An apple a day!");
    break;
  case "banana":
    console.log("Bananas are great.");
    break;
  default:
    console.log("Unknown fruit");
}

Conditions Inside Loops

Conditions are also used inside loops to break, skip, or control behavior.

for (let i = 1; i <= 5; i++) {
  if (i === 3) {
    continue; // Skip when i is 3
  }
  console.log(i);
}

Real-World Example: Form Validation

function validateForm(name, email) {
  if (!name || !email) {
    return "Name and email are required.";
  }

  if (!email.includes("@")) {
    return "Email must be valid.";
  }

  return "Form is valid!";
}

console.log(validateForm("Jada", "")); // Output: Name and email are required.

This example shows how conditions are used to handle common logic in real applications.