The height read-only property of the SVGFEFloodElement interface describes the vertical size of an SVG filter primitive as a SVGAnimatedLength.
It reflects the height attribute of the <feFlood> element, which fills an SVG filter subregion with the color and opacity defined by flood-color and flood-opacity. The attribute is a <length> or a <percentage> relative to the height of the filter region. The default value is 100%. The property value is a length in user coordinate system units.
const feFlood = document.querySelector("feFlood");
const verticalSize = feFlood.height;
console.log(verticalSize.baseVal.value); // the `height` valueSVGFEFloodElement.width<blend-mode> data typemix-blend-mode property