---
title: isUndefined
framework: javascriptcore
role: symbol
role_heading: Instance Property
path: javascriptcore/jsvalue/isundefined
---

# isUndefined

A Boolean value that indicates whether the instance corresponds to the JavaScript undefined value.

## Declaration

```swift
var isUndefined: Bool { get }
```

## Discussion

Discussion The JavaScript undefined value is used for variables that have not yet been assigned a value, for formal parameters in functions for which no actual parameter has been passed, and as the result of expressions or function calls that do not explicitly return a value. Note that undefined is not the same as null.

## See Also

### Determining the Type of a JavaScript Value

- [isNull](javascriptcore/jsvalue/isnull.md)
- [isBoolean](javascriptcore/jsvalue/isboolean.md)
- [isNumber](javascriptcore/jsvalue/isnumber.md)
- [isString](javascriptcore/jsvalue/isstring.md)
- [isObject](javascriptcore/jsvalue/isobject.md)
- [isArray](javascriptcore/jsvalue/isarray.md)
- [isDate](javascriptcore/jsvalue/isdate.md)
- [isSymbol](javascriptcore/jsvalue/issymbol.md)