> For the complete documentation index, see [llms.txt](https://boxlang.ortusbooks.com/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://boxlang.ortusbooks.com/boxlang-language/reference/built-in-functions/decision/isdefined.md).
# IsDefined
Determine whether a given variable reference exists.
For example:
* `isDefined( "luis" )` will test for the existence of an `lmajano` variable in any accessible scope.
* `isDefined( "variables.foo" )` will test for the existence of a `foo` variable in the `variables` scope.
* `isDefined( "brad.age" )` will test for the existence of an `age` key in the `brad` struct, in any accessible scope
## Method Signature
```
IsDefined(variable=[string])
```
### Arguments
| Argument | Type | Required | Description | Default |
| ---------- | -------- | -------- | ------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- | ------- |
| `variable` | `string` | `true` | The variable reference to test for existence. For security reasons, only dot-notation is supported. Struct/array bracket
notation
is not supported, nor is function invocation, etc.
| |
## Examples
### Using IsDefined
Checking for the existence of a `form` variable.
```java
...
```
### Scope Evaluation Order and Unscoped Variables
Beware of scope evaluation order when checking for an unscoped variable name.
[Run Example](https://try.boxlang.io/?code=eJwrLcrRc%2FP3V7BVUCoFMtPy85WsudLyi3JhomA2RLi8KLMkNb%2B0pKC0RENBybNYQR0orq6QkpqWmZeaYq%2BgpKCmkFnsAuFqgLTmKyloKmii6cSiBKRXA6QdyAeSSppKClYKSkogrQC9mS57)
```java
url.FOO = "url.foo";
form.FOO = "form.foo";
writeoutput( "Is 'foo' defined? " & isDefined( "foo" ) );
writeoutput( isDefined( "foo" ) ? " (" & foo & ")" : "" );
```
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.
[Run Example](https://try.boxlang.io/?code=eJyNjrsOgjAYhXee4uQMUBYfQFQS48LgpE6GQQSSJmBNL%2FH1TWGplRjH%2F9z%2Bb1D323AFe6XHlXHNKC1RYwsOk5MFRlazSKb7dNkfq7NPhb0ieWlpO%2BXs01kBVgYfdbRdLx9dWxIppDnMl4ie58ijoR%2FREoTwcyFWCubEGuTXFDeN3i3IHjWmRIz5H%2BEC3CxFXG8CzHSZ)
```java
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( "
" );
writeoutput( "Is 'submit' defined? " & isDefined( "submit" ) );
writeoutput( isDefined( "submit" ) ? " (" & submit & ")" : "" );
```
Result: Is 'form.submit' defined? YES (local\['form.submit']) Is 'submit' defined? YES(form.submit)
### Additional Examples
[Run Example](https://try.boxlang.io/?code=eJxVjbEOgkAQRGv3KzZXYcN9ALEwQmeLPXKDbiJ35m5PTAj%2FLtgYM81M8jLPWs5J%2FI0l1RjEw%2FEkeuc%2BeCcqwXPSTjHCK8lQ%2FLCCzRDiWEYkqOH9mpl21vIpOLAGvoKbN%2FqscEQLJY184HmptlZejue2WbdRJDUVTVEUdR6f%2F4YNfXWPjK%2BgIl7%2FNWbQB8M5Ojo%3D)
```java
// using isDefined with condition statement
if( isDefined( "form.reset" ) ) {
// Code to be Executed
}
str = {};
str.VALUE = "test";
writeDump( isDefined( "str.value" ) );
// true
```
## Related
* [ArrayIsEmpty](/boxlang-language/reference/built-in-functions/decision/arrayisempty.md)
* [arrayIsEmpty](https://github.com/ortus-boxlang/boxlang-docs/tree/v1.x/boxlang-language/reference/built-in-functions/decision/arrayIsEmpty.md)
* [Attempt](/boxlang-language/reference/built-in-functions/decision/attempt.md)
* [IsArray](/boxlang-language/reference/built-in-functions/decision/isarray.md)
* [IsBinary](/boxlang-language/reference/built-in-functions/decision/isbinary.md)
* [IsBoolean](/boxlang-language/reference/built-in-functions/decision/isboolean.md)
* [IsBoxSet](/boxlang-language/reference/built-in-functions/decision/isboxset.md)
* [IsClosure](/boxlang-language/reference/built-in-functions/decision/isclosure.md)
* [IsCustomFunction](/boxlang-language/reference/built-in-functions/decision/iscustomfunction.md)
* [IsDate](/boxlang-language/reference/built-in-functions/decision/isdate.md)
* [IsDateObject](/boxlang-language/reference/built-in-functions/decision/isdateobject.md)
* [IsDebugMode](/boxlang-language/reference/built-in-functions/decision/isdebugmode.md)
* [IsEmpty](/boxlang-language/reference/built-in-functions/decision/isempty.md)
* [IsFileObject](/boxlang-language/reference/built-in-functions/decision/isfileobject.md)
* [IsIPv6](/boxlang-language/reference/built-in-functions/decision/isipv6.md)
* [IsJSON](/boxlang-language/reference/built-in-functions/decision/isjson.md)
* [IsLeapYear](/boxlang-language/reference/built-in-functions/decision/isleapyear.md)
* [IsLocalHost](/boxlang-language/reference/built-in-functions/decision/islocalhost.md)
* [IsNull](/boxlang-language/reference/built-in-functions/decision/isnull.md)
* [IsNumeric](/boxlang-language/reference/built-in-functions/decision/isnumeric.md)
* [IsNumericDate](/boxlang-language/reference/built-in-functions/decision/isnumericdate.md)
* [IsObject](/boxlang-language/reference/built-in-functions/decision/isobject.md)
* [IsQuery](/boxlang-language/reference/built-in-functions/decision/isquery.md)
* [IsRange](/boxlang-language/reference/built-in-functions/decision/isrange.md)
* [IsSimpleValue](/boxlang-language/reference/built-in-functions/decision/issimplevalue.md)
* [IsStringBuilder](/boxlang-language/reference/built-in-functions/decision/isstringbuilder.md)
* [IsStruct](/boxlang-language/reference/built-in-functions/decision/isstruct.md)
* [IsValid](/boxlang-language/reference/built-in-functions/decision/isvalid.md)
* [IsXML](/boxlang-language/reference/built-in-functions/decision/isxml.md)
* [IsXmlAttribute](/boxlang-language/reference/built-in-functions/decision/isxmlattribute.md)
* [IsXMLDoc](/boxlang-language/reference/built-in-functions/decision/isxmldoc.md)
* [IsXMLElem](/boxlang-language/reference/built-in-functions/decision/isxmlelem.md)
* [IsXMLNode](/boxlang-language/reference/built-in-functions/decision/isxmlnode.md)
* [IsXMLRoot](/boxlang-language/reference/built-in-functions/decision/isxmlroot.md)
* [LSIsNumeric](/boxlang-language/reference/built-in-functions/decision/lsisnumeric.md)
* [structIsEmpty](/boxlang-language/reference/built-in-functions/decision/structisempty.md)
---
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