undefined

The global undefined property represents the primitive value undefined. It is one of JavaScript's "primitive types".

Value

The primitive value undefined.

Description

undefined is a property of the global object. That is, it is a variable in global scope.

undefined is a non-configurable, non-writable property.

A variable that has not been assigned a value is of type undefined. A method or statement also returns undefined if the variable that is being evaluated does not have an assigned value. A function returns undefined if a value was not explicitly returned.