code: function toValue(str, measurement, popperOffsets, referenceOffsets) {
    // separate value from unit
    var split = str.match(/((?:\-|\+)?\d*\.?\d*)(.*)/);
    var value = +split[1];
    var unit = split[2];
  
    // If it's not a number it's an operator, I guess
    if (!value) {
      return str;
    }
  
    if (unit.indexOf('%') === 0) {
      var element = void 0;
      switch (unit) {
        case '%p':
          element = popperOffsets;
          break;
        case '%':
        case '%r':
        default:
          element = referenceOffsets;
      }
  
      var rect = getClientRect(element);
      return rect[measurement] / 100 * value;
    } else if (unit === 'vh' || unit === 'vw') {
      // if is a vh or vw, we calculate the size based on the viewport
      var size = void 0;
      if (unit === 'vh') {
        size = Math.max(document.documentElement.clientHeight, window.innerHeight || 0);
      } else {
        size = Math.max(document.documentElement.clientWidth, window.innerWidth || 0);
      }
      return size / 100 * value;
    } else {
      // if is an explicit pixel unit, we get rid of the unit and keep the value
      // if is an implicit unit, it's px, and we return just the value
      return value;
    }
  }
docs: Converts a string containing value + unit into a px value number
  @function
  @memberof {modifiers~offset}
  @private
  @argument {String} str - Value + unit string
  @argument {String} measurement - `height` or `width`
  @argument {Object} popperOffsets
  @argument {Object} referenceOffsets
  @returns {Number|String}
  Value in pixels, or original string if no values were extracted