Type Checking & Conversion in JavaScript
From the JavaScript cheat sheet · Variables & Data Types · verified Jul 2026
Type Checking & Conversion
Checking and converting between types
javascript
// Type checking
typeof 'text' // 'string'
typeof 42 // 'number'
typeof true // 'boolean'
typeof undefined // 'undefined'
typeof null // 'object' (legacy bug)
typeof {} // 'object'
typeof [] // 'object'
Array.isArray([]) // true
// Type conversion
String(42) // '42'
Number('42') // 42
Boolean(1) // true
parseInt('42px') // 42
parseFloat('3.14') // 3.14💡 typeof null returns "object" - a known bug kept for compatibility
⚡ Use Array.isArray() to check for arrays, not typeof
📌 Prefer explicit conversion over implicit coercion
🔥 Falsy values: false, 0, "", null, undefined, NaN