The x read-only property of the SVGFESpecularLightingElement interface describes the horizontal coordinate of the position of an SVG filter primitive as a SVGAnimatedLength.
It reflects the x attribute of the <feSpecularLighting> element, which lights a source graphic using the alpha channel as a bump map. The attribute is a <length> or <percentage>. The <coordinate> is a length in the user coordinate system that is the given distance from the origin of the user coordinate system along the x-axis. If the x attribute is a percent value, the property value is relative to the width of the filter region in user coordinate system units. The default value is 0.
const feSpecularLighting = document.querySelector("feSpecularLighting");
const leftPosition = feSpecularLighting.x;
console.log(leftPosition.baseVal.value); // the `x` value