Scripting SVG using the native DOM interfaces is currently (2016) in a state of slight change. The current SVG standard (1.1) is implemented well by most major web browsers. However, as the SVG 2.0 standard is under development, some browsers have begun to remove SVG 1.1 features that will be obsolete in 2.0. You can see a full list of proposed changes from SVG 1.1 to SVG 2.0 in Appendix L of SVG 2.0.
In SVG 1.1
<path> elements are defined to have a
pathSegList property that gives access to a native representation of all path commands. Google Chrome v48 removed this property at the end of 2015, in preparation for a proposed replacement in SVG 2.0. Until SVG 2.0 support is added, you must use a polyfill to either get the 1.1 functionality back, or to implement the proposed 2.0 API.