How to use the web-streams-polyfill.ReadableStream function in web-streams-polyfill

buf[p++] = 0x50;
      buf[p++] = 0x45;
      buf[p++] = 0x32;
      buf[p++] = 0x2e;
      buf[p++] = 0x30;
      // Sub-block
      buf[p++] = 0x03;
      buf[p++] = 0x01;
      buf[p++] = loop_count & 0xff;
      buf[p++] = loop_count >> 8 & 0xff;
      buf[p++] = 0x00; // Terminator.
    }
    var self = this;
    var reader = rs.getReader();

    return new ReadableStream({
      start: function start(controller) {
        controller.enqueue(new Uint8Array(buf));
      },
      pull: function pull(controller) {
        return reader.read().then(function (_ref2) {
          var done = _ref2.done,
              value = _ref2.value;

          if (done) {
            controller.enqueue(new Uint8Array([0x3b]));
            controller.close();
            return;
          }

          self.addFrame.apply(self, [controller].concat(value));
        });

getStream(frames, ctx) {
    var options = this.options;
    var width = options.gifWidth;
    var height = options.gifHeight;
    var totalImages = frames.length;
    var processedImages = 0;
    var self = this;
    var rs = new ReadableStream({
      pull: function pull(controller) {
        var frame = frames.shift();
        if (!frame) controller.close();
        var imgData, rgbComponents, paletteRGB, nq, paletteArray, numberPixels, pixels;
        var r, g, b;
        var k = 0;
        var delay = (frame.delay) ? frame.delay / 10 : 100;
        processedImages++;
        delay = (processedImages === totalImages && options.extraLastFrameDelay) ? delay + (options.extraLastFrameDelay / 10) : delay;// Add an extra
        ctx = self.addFrameDetails(ctx, frame);
        imgData = ctx.getImageData(0, 0, width, height);
        rgbComponents = dataToRGB(imgData.data, imgData.width, imgData.height);
        nq = new NeuQuant(rgbComponents, rgbComponents.length, 15);
        paletteRGB = nq.process();
        paletteArray = new Uint32Array(componentizedPaletteToArray(paletteRGB));
        numberPixels = imgData.height * imgData.width;

function emptyStream() {
		return new ReadableStream({
			start(controller) {
				controller.close()
			}
		})
	}
}

function streamFromString(str) {
		return new ReadableStream({
			start(controller) {
				controller.enqueue(str)
				controller.close()
			},
			cancel() { },
			pull() { }
		})
	}

function _read(ref) {
		let closed = false
		return new ReadableStream({
			start(controller) {
				dispatcher.dispatch("readProxyStream",
					ref,
					new ivm.Reference((name, ...args) => {
						if (name === "close" || name === "end") {
							if (!closed) {
								closed = true
								controller.close()
							}
						} else if (name === "error") {
							controller.error(new Error(args[0]))
						} else if (name === "data") {
							controller.enqueue(args[0])
						} else
							logger.debug("unhandled event", name)
					})