The preserveAspectRatio read-only property of the SVGMarkerElement interface returns an SVGAnimatedPreserveAspectRatio object containing the value of the preserveAspectRatio attribute of the <marker>.

An SVGAnimatedPreserveAspectRatio object. The baseVal property of this object returns an SVGPreserveAspectRatio object, with the following properties:

align

One of the following numeric constants:

0

SVG_PRESERVEASPECTRATIO_UNKNOWN

1

SVG_PRESERVEASPECTRATIO_NONE

2

SVG_PRESERVEASPECTRATIO_XMINYMIN

3

SVG_PRESERVEASPECTRATIO_XMIDYMIN

4

SVG_PRESERVEASPECTRATIO_XMAXYMIN

5

SVG_PRESERVEASPECTRATIO_XMINYMID

6

SVG_PRESERVEASPECTRATIO_XMIDYMID

7

SVG_PRESERVEASPECTRATIO_XMAXYMID

8

SVG_PRESERVEASPECTRATIO_XMINYMAX

9

SVG_PRESERVEASPECTRATIO_XMIDYMAX

10

SVG_PRESERVEASPECTRATIO_XMAXYMAX

meetOrSlice

One of the following numeric constants:

0

SVG_MEETORSLICE_UNKNOWN

1

SVG_MEETORSLICE_MEET

2

SVG_MEETORSLICE_SLICE

This example demonstrates how to return the numeric constants for align and meetOrSlice which relate to the values set for the preserveAspectRatio attribute of <marker>.

<svg id="svg" viewBox="0 0 100 100" xmlns="http://www.w3.org/2000/svg">
  <defs>
    <marker
      id="arrow"
      viewBox="0 0 10 10"
      refX="5"
      refY="5"
      preserveAspectRatio="xMidYMid meet"
      markerWidth="6"
      markerHeight="6"
      orient="auto-start-reverse">
      <path d="M 0 0 L 10 5 L 0 10 z" />
    </marker>
  </defs>
</svg>

let marker = document.getElementById("arrow");
console.log(marker.preserveAspectRatio.baseVal.align); // 6
console.log(marker.preserveAspectRatio.baseVal.meetOrSlice); // 1