如何在writable.write函数内部使用“此”

Question

我需要访问writable.write函数中的一些类实例数据。下面是一段简短的类型记录代码，说明了我想要做的事情：

import * as socketio from 'socket.io'
import { Writable } from 'stream'

export class DataClient {
  public socket: socketio.Socket
  private writable: Writable

  constructor(socket: socketio.Socket) {
    this.socket = socket

    this.writable = new Writable({
      write: function (chunk, encoding, next) {
        this.socket.emit('data', chunk)
        next()
      }.bind(this),
    })
  }
}

我从ESLint得到以下错误：

any
'this' implicitly has type 'any' because it does not have a type annotation.ts(2683)
dataClient.ts(12, 14): An outer value of 'this' is shadowed by this container.

我尝试过使用<>和as进行转换，但这并没有什么不同。实际的代码更复杂，但这在最简单的情况下显示了问题。此外，虽然我可能只能引用套接字(参数)，但我还需要访问其他实例数据项，它们不是构造函数的参数。

有没有办法让TS知道"this“指的是DataClient实例？

Answer 1

您应该使用一个箭头函数来表示写方法，然后这将引用DataClient实例：

import * as socketio from "socket.io";
import { Writable } from "stream";

export class DataClient {
  public socket: socketio.Socket;
  private writable: Writable;

  constructor(socket: socketio.Socket) {
    this.socket = socket;

    this.writable = new Writable({
      write: (chunk, encoding, next) => {
        this.socket.emit("data", chunk);
        next();
      },
    });
  }
}

另一种解决方案是将函数指定为类的方法：

import * as socketio from "socket.io";
import { Writable } from "stream";

export class DataClient {
  public socket: socketio.Socket;
  private writable: Writable;

  constructor(socket: socketio.Socket) {
    this.socket = socket;

    this.writable = new Writable({
      write: this.writeFunc,
    });
  }

  writeFunc(chunk: any, encoding: BufferEncoding, next: any): void {
    this.socket.emit("data", chunk);
    next();
  }
}