What is the typeof operator?

The typeof operator returns a string indicating the type of the operand. Results: typeof "hello" → "string", typeof 42 → "number", typeof true → "boolean", typeof undefined → "undefined", typeof Symbol() → "symbol", typeof 42n → "bigint", typeof function(){} → "function", typeof {} → "object", typeof [] → "object", typeof null → "object" (historical bug). To check for arrays, use Array.isArray(value). To check for null: value === null. To check for an object (excluding null): typeof value === "object" && value !== null. instanceof checks the prototype chain: [] instanceof Array is true. Object.prototype.toString.call(value) gives the most accurate type string.