The flipX() method of the DOMMatrixReadOnly interface creates a new matrix being the result of the original matrix flipped about the x-axis.

Returns a DOMMatrix containing a new matrix being the result of the original matrix flipped about the x-axis, which is equivalent to multiplying the matrix by DOMMatrix(-1, 0, 0, 1, 0, 0). The original matrix is not modified.

In this example, the SVG contains two paths in the shape of a triangle, both drawn to the same position. Note that the x co-ordinate of the viewBox attribute is negative, showing us content from both sides of the x-axis.

The JavaScript first creates an identity matrix, then uses the flipX() method to create a new matrix, which is then applied to the blue triangle, inverting it across the x-axis. The red triangle is left in place.

HTML

<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>

JavaScript

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

Result