SVGPathElement: pathLength 属性

<svg width="200" height="100">
  <path id="myPath" d="M 0,30 h100" pathLength="50" />
</svg>

const pathElement = document.getElementById("myPath");

// Access the pathLength property
const animatedNumber = pathElement.pathLength;

// The base value of the pathLength attribute
console.log(animatedNumber.baseVal); // Output: 100