The y read-only property of the SVGRectElement interface describes the vertical coordinate of the position of an SVG rectangle as a SVGAnimatedLength. 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 y-axis. Its syntax is the same as that for <length>.
It reflects the <rect> element's y geometric attribute value. The CSS y property takes precedence over the SVG y attribute, so the value may not reflect the element's appearance. The default value is 0.
const rectangle = document.querySelector("rect");
const topPosition = rectangle.y;
console.log(topPosition.baseVal.value); // the `y` value