SVGGradientElement: href 属性

<svg xmlns="http://www.w3.org/2000/svg" width="200" height="200">
  <defs>
    <linearGradient id="gradient1">
      <stop offset="0%" stop-color="red" />
      <stop offset="100%" stop-color="blue" />
    </linearGradient>
    <linearGradient id="gradient2" href="#gradient1" />
  </defs>
  <rect x="10" y="10" width="180" height="180" fill="url(#gradient2)" />
</svg>

const gradient = document.getElementById("gradient2");
console.log(gradient.href.baseVal); // Output: "#gradient1"