Truthy and Falsy Values

Learn how JavaScript evaluates values as true or false in conditionals, with clear examples and explanations.

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Truthy and Falsy Values

What are Truthy and Falsy Values?

In JavaScript, when you use a value inside a condition, like in an if statement, JavaScript automatically converts that value to either true or false behind the scenes.

So, even if you're not using a true or false value directly, JavaScript decides to treat this value as true or as false.

Based on that decision, your condition either runs (if the value is truthy) or skips (if the value is falsy).

That doesn’t mean the value is exactly true or false, but JavaScript treats it like that when checking conditions.

Truthy Values

Anything that is not falsy is considered truthy.

Some common truthy values are:

  • true
  • Any number except 0 (like 1, -5, 3.14)
  • Any non-empty string (like "hello", "false", "0")
  • Dates
  • Symbols
  • BigInt values other than 0n
  • Arrays ([])
  • Objects ({})
  • Functions

Examples of Truthy Values:

if (true) {
  console.log("This will run!");
}
 
if ("hello") {
  console.log("This will run!");
}
 
if (123) {
  console.log("This will run!");
}
 
if (123456789n) {
  console.log("This will run!");
}
 
if ([]) {
  console.log("This will run!");
}

All these values are treated as true, so the code runs.

Falsy Values

Falsy values are values that evaluate to false when used in conditions.

Some common falsy values are:

  • false
  • 0 and -0
  • 0n
  • "" (Empty string)
  • null
  • undefined
  • NaN

Examples of Falsy Values:

if (false) {
  console.log("This will not run!");
}
 
if (0) {
  console.log("This will not run!");
}
 
if ("") {
  console.log("This will not run!");
}
 
if (null) {
  console.log("This will not run!");
}
 
if (NaN) {
  console.log("This will not run!");
}

All these values are treated as false, so the code will not run.

Examples

Example 1: Default value using OR operator

let username;
let displayName = username || "Guest";
 
console.log(displayName); // Output: "Guest"

Here,

  • The variable username is declared but not defined, which means it's undefined and undefined is a falsy value.
  • The || (OR) operator checks if username has a truthy value.
  • Since it's not a truthy value, it picks the next value, "Guest".
  • So, "Guest" gets assigned to displayName.

Example 2: Check for an empty string

let name = "";
 
if (!name) {
  console.log("Name is required");
}

Here,

  • The variable name is an empty string "", which is falsy.
  • !name means "not falsy", which becomes true in this case.
  • So, the code inside the if block runs and prints "Name is required".

Example 3: Empty array is truthy

let items = [];
 
if (items) {
  console.log("This will run!");
}

Here,

  • The variable items is an empty array.
  • Even though it’s empty, arrays are always truthy in JavaScript.
  • So, the condition is true, and "This will run!" is printed.

Example 4: Short-circuiting with AND operator

let isLoggedIn = true;
isLoggedIn && console.log("Welcome back!");

Here,

  • isLoggedIn is true (truthy), so the right side runs and prints Welcome back!.
  • If isLoggedIn were false, nothing would happen because false && anything stops right away.

Example 5: Using falsy value in a condition

let score = 0;
 
if (!score) {
  console.log("No score yet!");
}

Here,

  • 0 is a falsy value, so !score becomes true.
  • "No score yet!" is printed.

Example 6: Use OR operator to set the default text

let input = "";
let message = input || "Please enter something!";
 
console.log(message); // Output: "Please enter something!"

Here,

  • input is an empty string, which is a falsy value.
  • So the default "Please enter something!" is used.

Example 7: Truthy object check

let user = {};
 
if (user) {
  console.log("User exists!");
}

Here,

  • The variable user is an empty object.
  • Even though it’s empty, objects are always truthy in JavaScript.
  • So "User exists!" is printed.

Example 8: Double negation to get the real boolean

let value = "hello";
let isTruthy = !!value;
 
console.log(isTruthy); // Output: true

Here,

  • "hello" is a truthy value.
  • The first !value turns it into false.
  • The second ! turns it back to true.
  • This is a common trick to convert any value to its boolean form.

Example 9: "false" is truthy

if ("false") {
  console.log("This will run!");
}

Here, even though it says "false", it’s a non-empty string, so it’s truthy.

Example 10: "0" is truthy

if ("0") {
  console.log("This will run!");
}

Here,

  • "0" is a string containing the character zero.
  • In JavaScript, any non-empty string is truthy, even if it looks like a number.
  • Even though 0 (the number) is falsy, "0" (a non-empty string) is truthy.
  • That means the condition if ("0") is true, and the code inside the block will run.

Tip

If you're ever unsure whether a value is truthy or falsy, use:

console.log(Boolean(value));

Or the shorter version:

console.log(!!value);

This will convert the value into its actual boolean form.

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