DOMMatrixReadOnly: flipX() メソッド

  DOMMatrixReadOnly.flipX()

<svg width="100" height="100" viewBox="-50 0 100 100">
  <path fill="red" d="M 0 50 L 50 0 L 50 100 Z" />
  <path id="flipped" fill="blue" d="M 0 50 L 50 0 L 50 100 Z" />
</svg>

const flipped = document.getElementById("flipped");
const matrix = new DOMMatrixReadOnly();
const flippedMatrix = matrix.flipX();
flipped.setAttribute("transform", flippedMatrix.toString());