What does the typeof operator do in JavaScript?

In JavaScript, the `typeof` operator is used to determine the data type of a given expression or variable. It returns a string indicating the type of the operand. The syntax is as follows:

typeof operand

Here, `operand` is the expression or variable for which you want to determine the type.

Examples:

let x = 5;

console.log(typeof x);  // Outputs: "number"

let y = "Hello";

console.log(typeof y);  // Outputs: "string"

let z = true;

console.log(typeof z);  // Outputs: "boolean"

let obj = { key: "value" };

console.log(typeof obj);  // Outputs: "object"

Here's a summary of some common types and their corresponding `typeof` results:

- `typeof 42` returns "number".

- `typeof "hello"` returns "string".

- `typeof true` returns "boolean".

- `typeof {}` returns "object" (for objects and null).

- `typeof []` returns "object" (for arrays).

- `typeof undefined` returns "undefined".

- `typeof null` returns "object" (Note: This is a historical quirk in JavaScript, `null` is technically of type "object" according to `typeof`, but it's actually a primitive value and not an object).

It's important to note that `typeof` is a unary operator, and it doesn't always provide detailed information about complex objects or distinguish between different types of objects. For more detailed type checking, other methods like `instanceof` or checking the constructor property might be used.