Suggest an edit

Improve this article

Refine the answer for “Truthy/falsy values”. Your changes go to moderation before they’re published.

Approval required

Content

What you’re changing

Title (EN)

Short answer (EN)

Shown above the full answer for quick recall.

Answer (EN)

## Definition

In JavaScript, **any value** can be coerced to a logical type (`boolean`).

- If after coercion it becomes `true` -> it is a **truthy** value.
- If it becomes `false` -> it is a **falsy** value.

---

## Easy to check:

```javascript
Boolean(value) // returns true or false
!!value        // short equivalent
```

---

## List of all **falsy** values (8 total)

| Value | Description |
|---|---|
| `false` | false |
| `0` | the number zero |
| `-0` | negative zero |
| `0n` | BigInt zero |
| `""` | empty string |
| `null` | "nothing" |
| `undefined` | undefined |
| `NaN` | result of invalid numeric operations |

Everything else in JavaScript is **truthy**.

---

## Falsy examples

```javascript
Boolean(false);      // false
Boolean(0);          // false
Boolean('');         // false
Boolean(null);       // false
Boolean(undefined);  // false
Boolean(NaN);        // false
```

---

## Truthy examples

```javascript
Boolean(true);        // true
Boolean(1);           // true
Boolean('0');         // true (string, not empty)
Boolean('false');     // true (also a string)
Boolean([]);          // true (an empty array is still truthy)
Boolean({});          // true (empty object)
Boolean(function(){});// true (function)
```

---

## Example in an `if` condition

```javascript
if ('hello') {
  console.log('Runs');
}

if (0) {
  console.log('Does not run');
}
```

> Because `'hello'` -> truthy,
> and `0` -> falsy.

---

## Example with the `&&` operator

```javascript
console.log(true && 'JS'); // "JS" (both truthy)
console.log(false && 'JS'); // false (falsy stops it)
```

---

## Example with the `||` operator

```javascript
console.log('' || 'default'); // "default"
console.log('Hi' || 'default'); // "Hi"
```

> `||` returns the **first truthy value**.

---

## Example with double negation `!!`

```javascript
!!'text'     // true
!!0          // false
!![]         // true
!!null       // false
```

---

## Important: truthy is not "logically true" in the mathematical sense

JS does not "compare", it **coerces** values to `boolean`.

```javascript
'false' == true   // false
!!'false'         // true
```

> `'false'` is a string (truthy),
> but when compared to `true`, different logic applies (types are coerced first).

---

## Summary

| Type | Examples | Boolean value |
|---|---|---|
| **Falsy** | `false`, `0`, `-0`, `0n`, `""`, `null`, `undefined`, `NaN` | `false` |
| **Truthy** | `'0'`, `' '`, `'false'`, `[]`, `{}`, `function(){}` | `true` |

---

## In short

> **Truthy** - "behaves like `true`"
> **Falsy** - "behaves like `false`"

---

**Check:**

```javascript
if (value) {
  // runs if value is truthy
} else {
  // if value is falsy
}
```

Markdown · drag & drop images · ⌘B / ⌘I shortcuts419 words

For the reviewer

Note to the moderator (optional)

Visible only to the moderator. Helps review go faster.