What data types are there in JavaScript?

This question often stumps even senior developers, although it is actually very simple.

When you hear it, there's no need to overcomplicate things with answers like: there are arrays, objects, functions… - because from the data type perspective in JavaScript, all of these belong to a single non-primitive type - object.

Non-primitive type: object

Almost everything "complex" belongs to object:

1. { a: 1 } - an object
2. [1, 2, 3] - an array (but the type is still object)
3. new Date() - a date (also an object)
4. function () {} - a function (technically it is an object, but typeof returns function for it)

Primitive types (there are 7)

Besides object, JavaScript has 7 primitive types - they are not objects and don't have methods/properties like контейнери (although JS sometimes wraps them in wrapper objects under the hood).

1. string - strings: hello
2. number - numbers: 42, 3.14, NaN, Infinity
3. boolean - boolean type: true / false
4. null - empty value (an explicitly assigned absence of value)
5. undefined - value not assigned
6. symbol - unique identifiers: Symbol(id)
7. bigint - large integers: 123n

In total: 7 primitives + 1 non-primitive type, object. You can read about the difference between null and undefined at https://devs-hive.tech/interview-qa/null-vs-undefined-js.