new VRButton(container, scene, vrElementopt)
    A single button widget for toggling vr mode.
    Parameters:
| Name | Type | Attributes | Default | Description | 
|---|---|---|---|---|
| container | Element | String | The DOM element or ID that will contain the widget. | ||
| scene | Scene | The scene. | ||
| vrElement | Element | String | <optional> | document.body | The element or id to be placed into vr mode. | 
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Throws:
- 
        Element with id "container" does not exist in the document.
- Type
- DeveloperError
Members
container :Element
    Gets the parent container.
    Type:
- Element
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viewModel :VRButtonViewModel
    Gets the view model.
    Type:
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Methods
destroy()
    Destroys the widget.  Should be called if permanently
removing the widget from layout.
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isDestroyed() → {Boolean}
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Returns:
    true if the object has been destroyed, false otherwise.
- Type
- Boolean