Truthy and Falsy Values in JavaScript

In JavaScript, every value behaves like true or false when used inside conditions.
Understanding which values act as true (truthy) and which act as false (falsy) is important because conditions, loops, and many logical checks depend on this behavior.

College students and freshers often get confused by unexpected results in conditions, so this chapter will make the concept very simple.

What Are Truthy and Falsy Values?

When JavaScript expects a boolean (true/false), it automatically converts other values into true or false.

Falsy values ? Act as false

Truthy values ? Act as true

This conversion is called type coercion in boolean context.

Falsy Values (Only 7 in JavaScript)

There are exactly 7 falsy values:

1. false

2. 0

3. "" (empty string)

4. null

5. undefined

6. NaN

7. -0

Everything else is truthy.

Example: Checking falsy values

if (0) {
    console.log("True");
} else {
    console.log("False");
}

Output:

False

Because 0 is a falsy value.

Truthy Values

Any value that is not falsy is truthy.

Examples:

• "Hello"

• " " (space)

• "0" (string zero)

• 5

• -5

• [ ] (empty array)

• { } (empty object)

• true

Example: Checking truthy values

if ("Hello") {
    console.log("This is truthy");
} else {
    console.log("This is falsy");
}

Output:

This is truthy

Even an empty array {} or [] is truthy!

Why Is This Important?

Truthy and falsy values affect:

• Conditions

• Loops

• Input validations

• API responses

• Form handling

• Login checks

If you don’t understand them, you may get unexpected results.

Examples for Each Falsy Value

1. false

if (false) console.log("True"); else console.log("False");

Output:

False

2. 0

if (0) console.log("True"); else console.log("False");

Output:

False

3. "" (Empty string)

if ("") console.log("True"); else console.log("False");

Output:

False

4. null

if (null) console.log("True"); else console.log("False");

Output:

False

5. undefined

let a;
if (a) console.log("True"); else console.log("False");

Output:

False

6. NaN

if (NaN) console.log("True"); else console.log("False");

Output:

False

7. -0

if (-0) console.log("True"); else console.log("False");

Output:

False

Real-Life Example: Checking User Input

If the user enters nothing in a form:

let input = "";

if (input) {
    console.log("Valid input");
} else {
    console.log("Please enter something");
}

Output:

Please enter something

Because an empty string is falsy.

Real-Life Example: Checking a Login Value

let username = "rahul";

if (username) {
    console.log("Login Successful");
} else {
    console.log("Enter username");
}

Output:

Login Successful

Example Program With Multiple Truthy/Falsy Checks

let values = [0, 1, "", "Hello", null, undefined, [], {}];

for (let val of values) {
    if (val) {
        console.log(val, "? Truthy");
    } else {
        console.log(val, "? Falsy");
    }
}

Output:

0 ? Falsy
1 ? Truthy
 ? Falsy
Hello ? Truthy
null ? Falsy
undefined ? Falsy
[] ? Truthy
{} ? Truthy

This clearly shows how different values behave.

Common Mistakes Beginners Make

1. Thinking "0" is falsy (it is truthy).

2. Thinking empty arrays are falsy (they are truthy).

3. Using == instead of === (causes confusion with null/undefined).

4. Not checking user input properly.

5. Forgetting that NaN is falsy.

Practice Tasks (Do It Yourself)

1. Check whether a string is empty or not.

2. Check if a number is provided; otherwise show an error.

3. Print truthy or falsy for: 0, "0", [], {}, null, 45, "".

4. Create a login check where empty username should show an error.