getBlur (elem) {
    let val = 0
    if (elem) {
      const filterUrl = elem.getAttribute('filter')
      if (filterUrl) {
        const blur = getElement(elem.id + '_blur')
        if (blur) {
          val = blur.firstChild.getAttribute('stdDeviation')
        } else {
          const filterElem = getRefElem(filterUrl)
          const blurElem = getFeGaussianBlur(filterElem)
          if (blurElem !== null) {
            val = blurElem.getAttribute('stdDeviation')
          }
        }
      }
    }
    return val
  }
Gets the `stdDeviation` blur value of the given element.
@function module:svgcanvas.SvgCanvas#getBlur
@param {Element} elem - The element to check the blur value for
@returns {string} stdDeviation blur attribute value