calculate bbox union of selected svg elements

bbox-union.js

// example usage:
// bBoxUnion("svg > *") => Object {x: 464.9, y: 521.0, width: 319.75, height: 75.5}
function bBoxUnion(selector) {
  var nodeList = document.querySelectorAll(selector),
      nodeArray = Array.prototype.slice.call(nodeList);
      
  return nodeArray.reduce(function(memo, node) {
    if (node.getBBox) {
      var bBox = node.getBBox();
      memo.x = Math.max(memo.x, bBox.x);
      memo.y = Math.max(memo.y, bBox.y);
      memo.width = Math.max(memo.width, bBox.width);
      memo.height = Math.max(memo.height, bBox.height);
    } 
    return memo;
  }, { x: 0, y: 0, width: 0, height: 0 });
}