Excerpt from readline source library

readline.js

function Interface(input, output, completer, terminal) {
  if (!(this instanceof Interface)) {
    return new Interface(input, output, completer, terminal);
  }

  this._sawReturnAt = 0;
  this.isCompletionEnabled = true;
  this._sawKeyPress = false;
  this._previousKey = null;

  EventEmitter.call(this);
  var historySize;
  let crlfDelay;
  let prompt = '> ';

  if (input && input.input) {
    // an options object was given
    output = input.output;
    completer = input.completer;
    terminal = input.terminal;
    historySize = input.historySize;
    if (input.prompt !== undefined) {
      prompt = input.prompt;
    }
    crlfDelay = input.crlfDelay;
    input = input.input;
  }

  if (completer && typeof completer !== 'function') {
    throw new TypeError('Argument "completer" must be a function');
  }

  if (historySize === undefined) {
    historySize = kHistorySize;
  }

  if (typeof historySize !== 'number' ||
      isNaN(historySize) ||
      historySize < 0) {
    throw new TypeError('Argument "historySize" must be a positive number');
  }

  // backwards compat; check the isTTY prop of the output stream
  //  when `terminal` was not specified
  if (terminal === undefined && !(output === null || output === undefined)) {
    terminal = !!output.isTTY;
  }

  var self = this;

  this.output = output;
  this.input = input;
  this.historySize = historySize;
  this.crlfDelay = Math.max(kMincrlfDelay,
                            Math.min(kMaxcrlfDelay, crlfDelay >>> 0));

  // Check arity, 2 - for async, 1 for sync
  if (typeof completer === 'function') {
    this.completer = completer.length === 2 ? completer : function(v, cb) {
      cb(null, completer(v));
    };
  }

  this.setPrompt(prompt);

  this.terminal = !!terminal;

  function ondata(data) {
    self._normalWrite(data);
  }

  function onend() {
    if (typeof self._line_buffer === 'string' &&
        self._line_buffer.length > 0) {
      self.emit('line', self._line_buffer);
    }
    self.close();
  }

  function ontermend() {
    if (typeof self.line === 'string' && self.line.length > 0) {
      self.emit('line', self.line);
    }
    self.close();
  }

  function onkeypress(s, key) {
    self._ttyWrite(s, key);
    if (key && key.sequence) {
      // if the key.sequence is half of a surrogate pair
      // (>= 0xd800 and <= 0xdfff), refresh the line so
      // the character is displayed appropriately.
      const ch = key.sequence.codePointAt(0);
      if (ch >= 0xd800 && ch <= 0xdfff)
        self._refreshLine();
    }
  }

  function onresize() {
    self._refreshLine();
  }

  if (!this.terminal) {
    input.on('data', ondata);
    input.on('end', onend);
    self.once('close', function() {
      input.removeListener('data', ondata);
      input.removeListener('end', onend);
    });
    var StringDecoder = require('string_decoder').StringDecoder; // lazy load
    this._decoder = new StringDecoder('utf8');

  } else {

    emitKeypressEvents(input, this);

    // input usually refers to stdin
    input.on('keypress', onkeypress);
    input.on('end', ontermend);

    // Current line
    this.line = '';

    this._setRawMode(true);
    this.terminal = true;

    // Cursor position on the line.
    this.cursor = 0;

    this.history = [];
    this.historyIndex = -1;

    if (output !== null && output !== undefined)
      output.on('resize', onresize);

    self.once('close', function() {
      input.removeListener('keypress', onkeypress);
      input.removeListener('end', ontermend);
      if (output !== null && output !== undefined) {
        output.removeListener('resize', onresize);
      }
    });
  }

  input.resume();
}