Busboy中的.ON方法在哪里？

Question

我一直在查看Make-Middleware文件中Multer的源代码，并且遇到了附加到新的Busboy对象的.ON方法，所以我跳到了Busboy源代码，以查看。剂量完全做。

我尝试console.log busboy新对象，以查看对象中的所有方法，但.on方法确实显示了。

make-middleware.js

var Busboy = require('busboy');

var busboy;

try{
   busboy = new Busboy({
        headers: req.headers,
        limits: limits,
        preservePath: preservePath
      })
}catch(err){
return next(err);
}



    busboy.on('field', function (fieldname, value, fieldnameTruncated, valueTruncated) {
// code
});

busboy-＆gt; lib-＆gt; main.js：

var fs = require('fs'),
  WritableStream = require('stream').Writable || 
  require('readable-stream').Writable,
  inherits = require('util').inherits;

var parseParams = require('./utils').parseParams;

function Busboy(opts) {
  if (!(this instanceof Busboy))
    return new Busboy(opts);
  if (opts.highWaterMark !== undefined)
    WritableStream.call(this, {
      highWaterMark: opts.highWaterMark
    });
  else
    WritableStream.call(this);

  this._done = false;
  this._parser = undefined;
  this._finished = false;

  this.opts = opts;
  if (opts.headers && typeof opts.headers['content-type'] === 'string')
    this.parseHeaders(opts.headers);
  else
    throw new Error('Missing Content-Type');
}
inherits(Busboy, WritableStream);

Busboy.prototype.emit = function (ev) {
  if (ev === 'finish') {
    if (!this._done) {
      this._parser && this._parser.end();
      return;
    } else if (this._finished) {
      return;
    }
    this._finished = true;
  }
  WritableStream.prototype.emit.apply(this, arguments);
};

Busboy.prototype.parseHeaders = function (headers) {
  this._parser = undefined;
  if (headers['content-type']) {
    var parsed = parseParams(headers['content-type']),
      matched, type;
    for (var i = 0; i < TYPES.length; ++i) {
      type = TYPES[i];
      if (typeof type.detect === 'function')
        matched = type.detect(parsed);
      else
        matched = type.detect.test(parsed[0]);
      if (matched)
        break;
    }
    if (matched) {
      var cfg = {
        limits: this.opts.limits,
        headers: headers,
        parsedConType: parsed,
        highWaterMark: undefined,
        fileHwm: undefined,
        defCharset: undefined,
        preservePath: false
      };
      if (this.opts.highWaterMark)
        cfg.highWaterMark = this.opts.highWaterMark;
      if (this.opts.fileHwm)
        cfg.fileHwm = this.opts.fileHwm;
      cfg.defCharset = this.opts.defCharset;
      cfg.preservePath = this.opts.preservePath;
      this._parser = type(this, cfg);
      return;
    }
  }
  throw new Error('Unsupported content type: ' + headers['content-type']);
};

Busboy.prototype._write = function (chunk, encoding, cb) {
  if (!this._parser)
    return cb(new Error('Not ready to parse. Missing Content-Type?'));
  this._parser.write(chunk, cb);
};

var TYPES = [
  require('./types/multipart'),
  require('./types/urlencoded'),
];

module.exports = Busboy;

console.log（busbboy）：

<ref *1> Busboy {
  _writableState: WritableState {
    objectMode: false,
    highWaterMark: 16384,
    finalCalled: false,
    needDrain: false,
    ending: false,
    ended: false,
    finished: false,
    destroyed: false,
    decodeStrings: true,
    defaultEncoding: 'utf8',
    length: 0,
    writing: false,
    corked: 0,
    sync: true,
    bufferProcessing: false,
    onwrite: [Function: bound onwrite],
    writecb: null,
    writelen: 0,
    afterWriteTickInfo: null,
    buffered: [],
    bufferedIndex: 0,
    allBuffers: true,
    allNoop: true,
    pendingcb: 0,
    prefinished: false,
    errorEmitted: false,
    emitClose: true,
    autoDestroy: true,
    errored: null,
    closed: false
  },
  _events: [Object: null prototype] { field: [Function (anonymous)] },
  _eventsCount: 1,
  _maxListeners: undefined,
  _done: false,
  _parser: Multipart {
    _needDrain: false,
    _pause: false,
    _cb: undefined,
    _nparts: 0,
    _boy: [Circular *1],
    parser: Dicer {
      _writableState: [WritableState],
      _events: [Object: null prototype],
      _eventsCount: 4,
      _maxListeners: undefined,
      _bparser: [SBMH],
      _headerFirst: undefined,
      _dashes: 0,
      _parts: 0,
      _finished: false,
      _realFinish: false,
      _isPreamble: true,
      _justMatched: false,
      _firstWrite: true,
      _inHeader: true,
      _part: undefined,
      _cb: undefined,
      _ignoreData: false,
      _partOpts: {},
      _pause: false,
      _hparser: [HeaderParser],
      [Symbol(kCapture)]: false
    }
  },
  _finished: false,
  opts: {
    headers: {
      host: 'localhost:8080',
      connection: 'keep-alive',
      'content-length': '257644',
      'cache-control': 'max-age=0',
      'sec-ch-ua': '" Not A;Brand";v="99", "Chromium";v="101", "Google Chrome";v="101"',
      'sec-ch-ua-mobile': '?0',
      'upgrade-insecure-requests': '1',
      origin: 'http://localhost:8080',
      'content-type': 'multipart/form-data;',
      'user-agent': 'Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/101.0.4951.54 Safari/537.36',
      accept: 'text/html,application/xhtml+xml,application/xml;q=0.9,image/avif,image/webp,image/apng,*/*;q=0.8,application/signed-exchange;v=b3;q=0.9',
      'sec-fetch-site': 'same-origin',
      'sec-fetch-mode': 'navigate',
      'sec-fetch-user': '?1',
      'sec-fetch-dest': 'document',
      referer: 'http://localhost:8080/',
      'accept-encoding': 'gzip, deflate, br',
      'accept-language': 'en-US,en;q=0.9',
      'sec-gpc': '1'
    },
    limits: { fileSize: 1000000 },
  },
  [Symbol(kCapture)]: false
}