zoom.translateExtent()

zoom.translateExtent([extent])

If extent is specified, sets the translate extent to the specified array of points [[x0, y0], [x1, y1]], where [x0, y0] is the top-left corner of the world and [x1, y1] is the bottom-right corner of the world, and returns this zoom behavior. If extent is not specified, returns the current translate extent, which defaults to [[-∞, -∞], [+∞, +∞]]. The translate extent restricts panning, and may cause translation on zoom out. It is enforced on interaction and when using zoom.scaleBy, zoom.scaleTo and zoom.translateBy; however, it is not enforced when using zoom.transform to set the transform explicitly.