Why if([]) Returns True? Understanding Truthy & Falsy in JavaScript

What are Truthy and Falsy Values?

In JavaScript, every value can be treated as either true or false when used in a condition (if, while, ternary operator, etc.).

• Truthy values behave like true.
• Falsy values behave like false.

JavaScript automatically converts values to a boolean when evaluating conditions. This process is called Type Coercion.

---

Falsy Values

There are only a few falsy values in JavaScript:

false
0
-0
0n
""      // Empty string
null
undefined
NaN

Example

if (0) {
    console.log("This will run");
} else {
    console.log("0 is falsy");
}

Output:

0 is falsy

---

Truthy Values

Everything that is not falsy is truthy.

Examples:

true
1
-1
"hello"
"0"
[]
{}
function(){}

Example

if ("JavaScript") {
    console.log("String is truthy");
}

Output:

String is truthy

---

Common Interview Examples

Example 1: Non-empty String

let username = "Saravanan";

if (username) {
    console.log("Username exists");
}

Output:

Username exists

Because a non-empty string is truthy.

---

Example 2: Empty String

let username = "";

if (username) {
    console.log("Username exists");
} else {
    console.log("Username is empty");
}

Output:

Username is empty

Because an empty string is falsy.

---

Example 3: Checking Login Credentials

const username = "Saravanan";
const password = "1234";

if (username && password) {
    console.log("Login data available");
} else {
    console.log("Missing credentials");
}

Output:

Login data available

Both values are non-empty strings, so they are truthy.

---

Example 4: Empty Array

if ([]) {
    console.log("Array is truthy");
}

Output:

Array is truthy

Many beginners expect an empty array to be falsy, but it is truthy.

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Example 5: Empty Object

if ({}) {
    console.log("Object is truthy");
}

Output:

Object is truthy

An empty object is also truthy.

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Quick Reference Table

Value	Truthy/Falsy
false	Falsy
0	Falsy
""	Falsy
null	Falsy
undefined	Falsy
NaN	Falsy
1	Truthy
"hello"	Truthy
"0"	Truthy
[]	Truthy
{}	Truthy

---

Easy Rule to Remember

JavaScript has only a handful of falsy values. Everything else is truthy.

When in doubt, ask yourself:

Boolean(value)

Examples:

Boolean(0);        // false
Boolean("");       // false
Boolean("hello");  // true
Boolean([]);       // true
Boolean({});       // true

Understanding truthy and falsy values is essential because they are used extensively in conditions, loops, logical operators (&&, ||), and real-world application development.

References:
https://www.geeksforgeeks.org/javascript/explain-the-concept-of-truthy-falsy-values-in-javascript/
https://stackoverflow.com/questions/35642809/understanding-javascript-truthy-and-falsy
https://frontend.turing.edu/lessons/module-1/js-truthy-falsy-expressions.html