biobulkbende.org/node_modules/readable-stream/lib/_stream_passthrough.js

// Copyright Joyent, Inc. and other Node contributors.
//
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// "Software"), to deal in the Software without restriction, including
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//
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// a passthrough stream.
// basically just the most minimal sort of Transform stream.
// Every written chunk gets output as-is.

'use strict';

module.exports = PassThrough;

var Transform = require('./_stream_transform');

/*<replacement>*/
var util = Object.create(require('core-util-is'));
util.inherits = require('inherits');
/*</replacement>*/

util.inherits(PassThrough, Transform);

function PassThrough(options) {
  if (!(this instanceof PassThrough)) return new PassThrough(options);

  Transform.call(this, options);
}

PassThrough.prototype._transform = function (chunk, encoding, cb) {
  cb(null, chunk);
};