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# isUndefined

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

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

## 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`.

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