JavaScript Typeof Guide
The typeof operator returns a string indicating the type of an unevaluated operand. Essential for type checking and debugging. The guide walks through typeof Results. Returns: "undefined", "boolean", "number", "bigint", "string", "symbol", "function", "object". Null is "object" (historical bug). Array is "object". Use Array.isArray() for arrays. typeof NaN is "number". typeof document.all is "undefined". Use typeof for: checking if variable exists, primitive type checking, function detection. The guide is organized into 1 sections that build on each other, each pairing a prose explanation with runnable code. Related guides: Arrays, Strings, Numbers, Math, Date. This is one of 145 JavaScript guides on JS Reference — see the full list on the guides page. Practice what you learn in the JavaScript playground, and look up any unfamiliar term in the JavaScript glossary.