What is truthy and falsy in JavaScript

Short answer

In JavaScript, every value is either truthy or falsy. Falsy values coerce to false in boolean contexts, while truthy values coerce to true.

How it works

The six falsy values are:

• false
• 0 and -0 and 0n
• '' (empty string)
• null
• undefined
• NaN

Everything else is truthy, including:

• '0' and 'false' (non-empty strings)
• [] and {} (empty collections)
• Infinity

Example

if ('0') { console.log('truthy'); }  // logs truthy
if ([]) { console.log('truthy'); }   // logs truthy
if (!!'') { console.log('never'); }  // does not log

Why it matters

Relying on truthiness makes code concise but risky. Explicit checks like value != null or Array.isArray(arr) && arr.length > 0 avoid subtle bugs with empty objects and strings.