The undefined Value
The topics are:
The Script undefined Value
The undefined value is a special value used in some places to specify an absence of information. For example, accessing a property of a value which is not defined, or a local variable which has been declared but not initialized, yields the undefined value.
There is no way of referencing the undefined value in programs. Checking if a value is the undefined value can be done using the typeof operator:
typeof(value) == "undefined" -> true if value is undefined, false otherwise.
Methods of undefined
The only method of undefined is:
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Syntax |
Effect |
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Returns the string "undefined". |
