How many data types are there in JS, and what are they?

Question

I started reading a book, Javascript for Kids. In it the author states that there are three data types:

• numbers
• strings
• booleans

However, according to W3Schools, there are four:

• numbers
• strings
• arrays
• objects

I wanted to know which one is correct.

Answer 1

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

Answer 2

Things aren't actually as straightforward as they described in answers above... they usually aren't in javascriptland ;)

typeof is the 'official' function that one uses to get the type in javascript, however in certain cases it might yield some unexpected results ...

1. Strings

typeof "String" or
typeof Date(2011,01,01)

"string"

2. Numbers

typeof 42 or
typeof NaN, lol

"number"

3. Bool

typeof true (valid values true and false)

"boolean"

4. Object

typeof {} or
typeof [] or
typeof null or
typeof /aaa/ or
typeof Error()

"object"

5. Function

typeof function(){}

"function"

6. Undefined

var var1; typeof var1

"undefined"

Alternative is to use ({}).toString() which will get you somewhat more accurate answer most of the time...