То, что я достиг:
// Get the id of the <path> element and the length of <path>
var myline = document.getElementById("myline");
var length = myline.getTotalLength();
circle = document.getElementById("circle");
// The start position of the drawing
myline.style.strokeDasharray = length;
// Hide the triangle by offsetting dash. Remove this line to show the triangle before scroll draw
myline.style.strokeDashoffset = length;
// Find scroll percentage on scroll (using cross-browser properties), and offset dash same amount as percentage scrolled
window.addEventListener("scroll", myFunction);
function myFunction() {
// What % down is it?
var scrollpercent = (document.body.scrollTop + document.documentElement.scrollTop) / (document.documentElement.scrollHeight - document.documentElement.clientHeight);
// Length to offset the dashes
var draw = length * scrollpercent;
// Reverse the drawing (when scrolling upwards)
myline.style.strokeDashoffset = length - draw;
//get point at length
endPoint = myline.getPointAtLength(draw);
circle.setAttribute("cx", endPoint.x);
circle.setAttribute("cy", endPoint.y);
}
body {
height: 2000px;
background: #f1f1f1;
}
#circle {
fill: red;
}
#mySVG {
position: absolute;
top: 15%;
width: 100%;
height: 1000px;
}
.st1 {
fill: none;
stroke-dashoffset: 3px;
stroke: grey;
stroke-width: 4;
stroke-miterlimit: 10;
stroke-dasharray: 20;
}
.st0 {
fill: none;
stroke-dashoffset: 3px;
stroke: red;
stroke-width: 5;
stroke-miterlimit: 10;
stroke-dasharray: 20;
}
<svg id="mySVG" viewBox="0 0 60 55" preserveAspectRatio="xMidYMin slice" style="width: 6%; padding-bottom: 42%; height: 1px; overflow: visible">
<path class="st1" stroke-dasharray="10,9" d="M 20 0 v 20 a 30 30 0 0 0 30 30 h 600 a 40 40 0 0 1 0 80 h -140 a 30 30 0 0 0 0 60 h 200 a 40 40 0 0 1 0 80 h -100 a 30 30 0 0 0 -30 30 v 20" /> Sorry, your browser does not support inline SVG.
</svg>
<svg id="mySVG" viewBox="0 0 60 55" preserveAspectRatio="xMidYMin slice" style="width: 6%; padding-bottom: 42%; height: 1px; overflow: visible">
<circle id="circle" cx="10" cy="10" r="10"/>
<path id="myline" class="st0" stroke-dasharray="10,9" d="M 20 0 v 20 a 30 30 0 0 0 30 30 h 600 a 40 40 0 0 1 0 80 h -140 a 30 30 0 0 0 0 60 h 200 a 40 40 0 0 1 0 80 h -100 a 30 30 0 0 0 -30 30 v 20" /> Sorry, your browser does not support inline SVG.
</svg>