isDefined

Evaluates a string value to determine whether the variable named in it exists.

isDefined(variable_name) → returns boolean

Argument Reference

variable_name string
Required

A string expression containing the name of a variable to check the existence of. Only simple dotted notation is supported (for example myVar, arguments.myArg, myStruct.key). Square bracket notation to reference array elements or struct keys is not supported.

Links more information about isDefined

structKeyExists() vs isDefined() - An Adobe Forums discussion on the differences between structKeyExists() and isDefined().
Variable Naming Rules - Adobe Documentation defining valid variable names

Examples
Sample code invoking the isDefined function

Using IsDefined

Checking for the existence of a form variable.

<cfif isDefined("form.submit")>...</cfif>

Scope Evaluation Order and Unscoped Variables

Beware of scope evaluation order when checking for an unscoped variable name.

url.foo = "url.foo" ; form.foo = "form.foo"; writeoutput("Is 'foo' defined? " & isDefined("foo")); writeoutput(isDefined("foo") ? " (" & foo & ")" : "");

Expected Result: Is 'foo' defined? YES (url.foo)

Dot-notation Variable Names

Potentially unexpected behavior when checking for a dot-notation variable containing a scope name.

local["form.submit"] = "local['form.submit']" ; form.submit = "form.submit"; writeoutput("Is 'form.submit' defined?" & isDefined("form.submit")); writeoutput(isDefined("form.submit") ? " (" & form.submit & ")" : ""); writeoutput("<br>"); writeoutput("Is 'submit' defined? " & isDefined("submit")); writeoutput(isDefined("submit") ? " (" & submit & ")" : "");

Expected Result: Is 'form.submit' defined? YES (local['form.submit']) Is 'submit' defined? YES(form.submit)

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