A revamped version of https://gist.github.com/charliepark/a124b768c4db4ff3404d

BalancedMeasures2.js

var BalancedMeasures = {
  minimumScreenSizeToRunOn: 992,
  classNameToBalance: "graf--pullquote",

  run: function(classToRunOn){
    if(this.onSmallerScreen()){return;}
    var elements = this.getElementsToBalance(classToRunOn);
    for(var i = 0; i < elements.length; i++){
      this.balance(elements[i]);
    }
  },

  onSmallerScreen: function(){
    var body = document.getElementsByTagName("body")[0];
    var bodyWidth = parseFloat(window.getComputedStyle(body, null).getPropertyValue('width'));
    return bodyWidth < this.minimumScreenSizeToRunOn;
  },

  getElementsToBalance: function(classToRunOn){
    if(typeof(classToRunOn) === 'undefined'){classToRunOn = this.classNameToBalance;}
    return document.getElementsByClassName(classToRunOn);
  },

  balance: function(element){
    var originalStyle   = window.getComputedStyle(element);
    var originalHeight  = parseInt(originalStyle.height, 10);
    var originalWidth   = parseInt(originalStyle.width, 10);
    var originalMargins = parseInt(originalStyle.marginLeft, 10);
    var originalTransition = originalStyle.transition;
    var height          = originalHeight;
    var width           = originalWidth;
    var boxCanBeShrunk  = true;
    var boxIsTooTall    = false;
    var differenceInMarginWidth, newMargin;
    element.style.transition = "";
    while(boxCanBeShrunk){
      width = width - 100;
      element.style.width = ""+width+"px";
      height = parseInt(window.getComputedStyle(element).height, 10);
      if(height > originalHeight){
        boxCanBeShrunk = false;
        boxIsTooTall = true;
      }
    }
    while(boxIsTooTall){
      width = width + 10;
      element.style.width = ""+width+"px";
      height = parseInt(window.getComputedStyle(element).height, 10);
      if(height <= originalHeight){
        boxIsTooTall = false;
      }
    }
    differenceInMarginWidth = (originalWidth - width)/2;
    newMargin = originalMargins + differenceInMarginWidth;
    element.style.marginLeft = ""+newMargin+"px";
    element.style.marginRight = ""+newMargin+"px";
    element.style.transition = originalTransition;
  }
};