The width read-only property of the SVGFEConvolveMatrixElement interface describes the horizontal size of an SVG filter primitive as a SVGAnimatedLength.
It reflects the <feConvolveMatrix> element's width filter primitive attribute. The <feConvolveMatrix> filter applies a matrix convolution effect, combining pixels in the input image with neighboring pixels to produce a convolution effect such as blurring, edge detection, sharpening, embossing or beveling. 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 feConvolveMatrix = document.querySelector("feConvolveMatrix");
const horizontalSize = feConvolveMatrix.width;
console.log(horizontalSize.baseVal.value); // the `width` valueSVGFEConvolveMatrixElement.height<filter> element, SVG filter attribute in SVG