ByteLengthQueuingStrategy: метод size()

size(chunk)

const queuingStrategy = new ByteLengthQueuingStrategy({ highWaterMark: 1 });

const readableStream = new ReadableStream(
  {
    start(controller) {
      // …
    },
    pull(controller) {
      // …
    },
    cancel(err) {
      console.log("stream error:", err);
    },
  },
  queuingStrategy,
);

const size = queueingStrategy.size(chunk);