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Minimal dependency-free pan/zoom library

  <div id="viewport">
    <div id="content">
      <!-- your pan/zoomable content here -->

    const tragopan = new Tragopan({
      viewport: document.querySelector('#viewport'),
      content: document.querySelector('#content')


  • Vanilla JavaScript
  • Just ~200 source lines of code
  • Minified gzip'd payload is about 1.6k
  • Fast -- uses native browser scrolling for panning
  • Focal zooming in/out based on mouse pointer position
  • Options for panning with space-drag, zooming with scroll
  • Made with ❤️ at

How it works

Tragopan uses native browser scrolling as its implementation for panning (left/right/up/down), and transform/scale for zooming (in/out). In our testing, we found that native scrolling was far more efficient than using transform for panning. As an extra bonus, if your DOM is structured so that your viewport element can be your document body, some browsers appear to do even more optimization for that special case.


new Tragopan(options)

Instantiate a pan/zoomable tragopan instance, given a viewport and a nested content element. Options include:

  • viewport: reference to a top-level element which will contain content to be panned and zoomed
  • content: a child element of the viewport
  • scaleIncrement: percentage by which zooming in or out one click should change the scale (default 0.04)
  • scrollZoom: enable bare scrolling to zoom, rather than ctrl/option-scroll to zoom (default false)
  • spacePan: enable panning via holding down the space bar (default false)
  • minScale: minimum zoom scale factor (default 0.5)
  • maxScale: maximum zoom scale factor (default 4)


Configure a tragopan instance with any options accepted by the constructor above.

tragopan.pan(x, y)

Pan to the given x and y coordinates in content space.

tragopan.zoom(scale[, focalPoint])

Zoom to the given scale, keeping the given focal point in-place on the screen. Focal point should be an object with x and y coordinates in content space. If focal point is ommitted, the center point of the viewport is used instead.


Zoom in by the given scaleIncrement if provided, or else zoom in by the configured/default scaleIncrement.


Zoom out by the given scaleIncrement if provided, or else zoom out by the configured/default scaleIncrement.

Pan to the center of the content


Pan to the center of the content

tragopan.on(eventName, handlerFn)

Register an event handler to be called when some panning or zooming event occurs. See below for more info.



Fired when a pan may be starting as a result of the user mousing-down on the viewport. A pan may or may not follow, with a click being a possible alternative conclusion.


Fired when the content moves relative to the viewport, whether from a click-drag, from a call to zoom(), or from a native scroll mouse event.


Fired when a pan via click-drag ends with a mouse-up.


Fired when the scale changes, either from a call to zoom(), or from a native ctrl/option-scroll mouse event.


Fired when any event above occurs.