<!--
title: Falsy vs null checks
domain: observability
topic: Null Handling
language: TSX
source: langfuse/langfuse
updated: 2025-06-25
url: https://awesomereviewers.com/reviewers/langfuse-falsy-vs-null-checks/
-->

Distinguish between falsy values (0, '', false, null, undefined) and null/undefined values in your code. Use explicit checks for null/undefined when you want to preserve other falsy values.

For absence checks, use:
```typescript
// Instead of !value (catches all falsy values including 0, '', false)
if (value === undefined || value === null) { /* or simply: value == null */ }
```

For providing defaults, use the nullish coalescing operator:
```typescript
// Instead of value || defaultValue (replaces all falsy values)
const result = value ?? defaultValue; // Only replaces null/undefined
```

For filtering collections, be specific about what you're filtering:
```typescript
// Instead of .filter(Boolean) (removes all falsy values)
array.filter(item => item != null); // Only removes null/undefined
```

When working with math operations on potentially empty collections:
```typescript
// Provide a default to avoid -Infinity/Infinity
Math.max(0, ...array.map(item => item.value));
```

For browser APIs and nested objects:
```typescript
// Check existence before accessing properties
const available = typeof window !== "undefined" && window.Feature?.isEnabled;
```