makeSvgController.js

module.exports = makeSvgController;
module.exports.canAttach = isSVGElement;

function makeSvgController(svgElement, options) {
  if (!isSVGElement(svgElement)) {
    throw new Error('svg element is required for svg.panzoom to work');
  }

  var owner = svgElement.ownerSVGElement;
  if (!owner) {
    throw new Error(
      'Do not apply panzoom to the root <svg> element. ' +
      'Use its child instead (e.g. <g></g>). ' +
      'As of March 2016 only FireFox supported transform on the root element');
  }

  if (!options.disableKeyboardInteraction) {
    owner.setAttribute('tabindex', 0);
  }

  var api = {
    getBBox: getBBox,
    getScreenCTM: getScreenCTM,
    getOwner: getOwner,
    applyTransform: applyTransform,
    initTransform: initTransform
  };
  
  return api;

  function getOwner() {
    return owner;
  }

  function getBBox() {
    var boundingBox =  svgElement.getBBox();
    return {
      left: boundingBox.x,
      top: boundingBox.y,
      width: boundingBox.width,
      height: boundingBox.height,
    };
  }

  function getScreenCTM() {
    var ctm = owner.getCTM();
    if (!ctm) {
      // This is likely firefox: https://bugzilla.mozilla.org/show_bug.cgi?id=873106
      // The code below is not entirely correct, but still better than nothing
      return owner.getScreenCTM();
    }
    return ctm;
  }

  function initTransform(transform) {
    var screenCTM = svgElement.getCTM();

    // The above line returns null on Firefox
    if (screenCTM === null) {
      screenCTM = document.createElementNS("http://www.w3.org/2000/svg", "svg").createSVGMatrix();
    }

    transform.x = screenCTM.e;
    transform.y = screenCTM.f;
    transform.scale = screenCTM.a;
    owner.removeAttributeNS(null, 'viewBox');
    svgElement.style.setProperty('transform', 'matrix(var(--pz-transform))');
  }

  function applyTransform(transform) {
    svgElement.style.setProperty('--pz-transform', 
    `${transform.scale}, 0, 0, ${transform.scale}, ${transform.x}, ${transform.y}`);
  }
}

function isSVGElement(element) {
  return element && element.ownerSVGElement && element.getCTM;
}