The width read-only property of the SVGFEDiffuseLightingElement interface describes the horizontal size of an SVG filter primitive as a SVGAnimatedLength.
It reflects the <feDiffuseLighting> element's width filter primitive attribute. The filter lights an image using the alpha channel as a bump map. The attribute is a <length> or a <percentage> relative to the width of the filter region. The default value is 100%. The property value is a length in user coordinate system units.
const feDiffuseLighting = document.querySelector("feDiffuseLighting");
const horizontalSize = feDiffuseLighting.width;
console.log(horizontalSize.baseVal.value); // the `width` valueSVGFEDiffuseLightingElement.heightSVGFESpecularLightingElement<feSpecularLighting><blend-mode> data typemix-blend-mode property