Null and Undefined
null represents the absence of a value.
null is not a default value for a variable. It represents an intentional choice, potentially signifying the absence of data in correctly functioning code.
undefined also corresponds to a non-value. However, unlike null, it represents the value of uninitialized variables, or parameters that have no value associated with them.
You can think of null values as non-error representations of nothing, whereas undefined usually corresponds to the lack of a value that was expected.
var nope; // undefined
nope = null; // null