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Version: 3.13.0


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


The primitive value undefined.


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.