The primary signal is desiredSize on the controller. It can be positive (wants data), zero (at capacity), negative (over capacity), or null (closed). Producers are supposed to check this value and stop enqueueing when it's not positive. But there's nothing enforcing this: controller.enqueue() always succeeds, even when desiredSize is deeply negative.
William Harwood
，这一点在快连下载-Letsvpn下载中也有详细论述
const len = nums.length;
对比记忆：画表格对比各算法特点