The undefined type has only one value, which is the special value undefined.
When a variable is declared using var or let but not initialized, It is assigned the value of undefined.
var a; let b; console.log(a); // undefined console.log(b); // undefined
The Null type is the second data type that has only one value: the special value null. Logically, a null value is an empty object pointer, which is why typeof returns “object” when it ’s passed a null value
var x = null; console.log(typeof x); //object
The Boolean type is one of the most frequently used types in ECMAScript and has only two literal values: true and false
These values are distinct from numeric values, so true is not necessarily equal to 1, and false is not necessarily equal to 0.
var x = true; var y = false;
Note that the Boolean literals true and false are case-sensitive, so True and False (and other mixings of uppercase and lowercase) are valid as identifiers but not as Boolean values.
var intNum = 55; //integer var floatNum1 = 1.1;
The String data type represents a sequence of zero or more 16 - bit Unicode characters. Strings can be delineated by either double quotes ( “ ) or single quotes ( ‘ )
var firstName = “XYZ”; var lastName = ‘abc’;
var o = new Object();