JAVASCRIPT

difference between undefined and null?

null is a special object because typeof null returns 'object'. 
On the other hand,
undefined means that the variable has not been declared,
or has not been given a value.

what is the difference between null and undefined

Undefined  used for unintentionally missing values.

Null       used for intentionally missing values. 

null vs undefined

//loosely equal (compare values between two variables)
null == undefined // true  ( null => 0 , undefined => NAN)

//strictly not equal (compare both type and value) 
null === undefined // false  (typeof null => object , typeof undefined => undefined)
null !== undefined // true   (typeof null => object , typeof undefined => undefined) 

difference between undefined and null

null == undefined