Path2D.addPath()

var canvas = document.getElementById("canvas");
var ctx = canvas.getContext("2d");

// Create a new path with a rect
var p1 = new Path2D();
p1.rect(0,0,100,100);

// Create another path with a rect
var p2 = new Path2D();
p2.rect(0,0,100,100);

// Create transformation matrix that moves vertically 300 points to the right
var m = document.createElementNS("http://www.w3.org/2000/svg", "svg").createSVGMatrix();
m.a = 1; m.b = 0;
m.c = 0; m.d = 1;
m.e = 300; m.f = 0;

// add the second path to the first path
p1.addPath(p2, m);

// Finally, fill the first path onto the canvas
ctx.fill(p1);