an example counting stream

下面是一个可读流的简单例子，依次触发读取 1 到 1,000,000：

const { Readable } = require('stream');
class Counter extends Readable {
  constructor(opt) {
    super(opt);
    this._max = 1000000;
    this._index = 1;
  }
  _read() {
    const i = this._index++;
    if (i > this._max)
      this.push(null);
    else {
      const str = String(i);
      const buf = Buffer.from(str, 'ascii');
      this.push(buf);
    }
  }
}