JS: Difference Between null vs undefined
undefined
is the value when a variable isn't assigned, property doesn't exist, value of function that doesn't have return statement, value of function args not given, out of bound array access, etc. See: undefined
.
null
is the value of a object's internal slot [[prototype]] when the object doesn't have a parent.
〔see Prototype and Inheritance〕
JavaScript the language does not restrict how you use null
or undefined
.
In general, you can pass undefined
as argument in function call, as if no argument is given.
You can also use null
as initial value of a variable.