Occurs when the size the width or height of this viewer's viewport (current view area) has changed.

You can use ThisWindow.ViewportWidth and ThisWindow.ViewportHeight to determine the new viewport size. Or, you can call ThisWindow.GetCurrentVisibleAreaRootSpace to get the viewport dimensions in the coordinate space the root visual of the display.

public event EventHandler ViewportSizeChanged

Public Event ViewportSizeChanged As EventHandler

JScript does not support events.