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# JSValueIsInstanceOfConstructor(_:_:_:_:)

Tests whether a JavaScript value is an object that the specified constructor creates.

```
func JSValueIsInstanceOfConstructor(_ ctx: JSContextRef!, _ value: JSValueRef!, _ constructor: JSObjectRef!, _ exception: UnsafeMutablePointer<JSValueRef?>!) -> Bool
```

## Parameters

`ctx`

The execution context to use.

`value`

The [`JSValueRef`](/documentation/JavaScriptCore/JSValueRef) to test.

`constructor`

The constructor to test against.

`exception`

A pointer to a [`JSValueRef`](/documentation/JavaScriptCore/JSValueRef) to store an exception in, if any. Pass `NULL` to discard any exception.

## Return Value

<doc://com.apple.documentation/documentation/Swift/true> if the value is an object that `constructor` creates, according to the JavaScript `instanceof` operator; otherwise, <doc://com.apple.documentation/documentation/Swift/false>.

## Discussion

---

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