Multiple WS2811 strips

Something like this? Assuming 10 LEDs in the first string:

var rgb = new Uint8ClampedArray(25*3);

 require("neopixel").write(B15, new Uint8Array(rgb.buffer, 0, 10*3));
 require("neopixel").write(other_pin, new Uint8Array(rgb.buffer, 10*3));