<!DOCTYPE html>
<head>
<script>
function go() {
var path = document.getElementById("myPath");
var len = path.getTotalLength();
console.log(len);
}
</script>
</head>
<body onload="go()">
<svg>
<path id="myPath" d="M45,-17592186044414A71,23 46,0,0 16382,98"/>
</svg>
</body>