You can test it using typeof operator:

The typeof operator gives you the names of data types when placed before any single operand.

Hence, try using typeof with any operand variable: it will give one of the following datatype names:

1. String
2. Number
3. Boolean
4. Object
5. Undefined

Hence, these are the five data Types in Javascript.

var val1 = "New World";   //returns String
var val2 = 5;             //returns Number
var val3 = true;          //returns Boolean
var val4 = [1,2,3];       //returns Object
var val5 = null;          //returns Object (Value is null, but type is still an object)
var val6;                 //returns Undefined

The current edition of the ECMAScript spec defines 8 value types:

1. Undefined
2. Null
3. Boolean
4. String
5. Symbol
6. Number
7. BigInt
8. Object

https://262.ecma-international.org/11.0/#sec-ecmascript-language-types

The typeof operator is a big source of confusion in JavaScript, because what it returns is not always the actual type of the value. The conversion table for typeof (https://262.ecma-international.org/11.0/#sec-typeof-operator) is like this

Note the two exceptions marked with !!!

To confuse us further, the language also provides wrapper functions for these 4 primitive types

1. Boolean
2. Number
3. String
4. BigInt

These functions

• when called with new, return their argument converted to a corresponding wrapper object (Boolean, Number etc)

• when called without new, return their argument converted to a corresponding primitive value (Boolean, Number etc)

These functions are also called implicitly (in the new or "constructor" mode) when a primitive is used in the "object" context (e.g. "foo".length)