coldfusion Variables Checking if a Variable Exists
Example
You can check if a variable has been defined in a scope by using ColdFusion's built in StructKeyExists() function. This can be used inside a <cfif> tag to prevent error messages in the event you attempt to refer to a variable that does not exist. You can also use this function to determine whether a user has performed a certain action or not. The syntax for the function is
StructKeyExists(structure, "key")
The following example checks if the variable firstName exists in the variables scope.
<cfif StructKeyExists(variables, "firstName")>
Hello #variables.firstname#!
<cfelse>
Hello stranger!
</cfif>
Alternatively, you may use the function:
isDefined("scopeName.varName")
To avoid ambiguity, it is recommended to declare the scope. For example, If you have a variable in the scope test
<cfset test.name = "Tracy" />
and you test for name in the global scope, you will get a result of true.
isDefined("name") <!--- true --->
isDefined("x.name") <!--- false--->
isDefined("test.name") <!--- true --->
