How to use the preconditions.singleton function in preconditions

'use strict';

var _ = require('lodash');
var $ = require('preconditions').singleton();
var sjcl = require('sjcl');

var Bitcore = require('bitcore');
var Address = Bitcore.Address;
var PrivateKey = Bitcore.PrivateKey;
var PublicKey = Bitcore.PublicKey;
var crypto = Bitcore.crypto;
var encoding = Bitcore.encoding;
var Utils = require('./utils');

function WalletUtils() {};

/* TODO: It would be nice to be compatible with bitcoind signmessage. How
 * the hash is calculated there? */
WalletUtils.hashMessage = function(text) {
  $.checkArgument(text);

var mdb = require('../lib/MessageDb').default();
var logger = require('../lib/logger').logger;
var preconditions = require('preconditions').singleton();
var microtime = require('microtime');
var cron = require('cron');
var CronJob = cron.CronJob;
var Threshold = (process.env.CLEANER_THRESHOLD_DAYS || 30) *24*60*60; // in seconds

module.exports.init = function(config) {
  var cronTime = config.cronTime || '0 * * * *';
  logger.info('Using cleaner plugin with cronTime ' + cronTime + ' and threshold of ' + Threshold + ' seconds');
  var onTick = function() {
    var limit = microtime.now() - 1000 * 1000 * Threshold;
    mdb.removeUpTo(limit, function(err, n) {
      if (err) logger.error(err);
      else logger.info('Ran cleaner task, removed ' + n);
    });
  };
  var job = new CronJob({

'use strict';

var Message = require('./Message');
var ECIES = require('./ECIES');
var preconditions = require('preconditions').singleton();
var Key = require('./Key');


var majorVersion = 1;
var minorVersion = 0;

/* Encrypted, authenticated messages to be shared between copayers */
var AuthMessage = function() {};

AuthMessage.setVersion = function(major, minor) {
  majorVersion = major;
  minorVersion = minor;
};

AuthMessage.encode = function(topubkey, fromkey, payload, opts) {
  preconditions.checkArgument(fromkey instanceof Key, 'fromkey');

var _ = require('lodash');
var async = require('async');
var $ = require('preconditions').singleton();

var log = require('npmlog');
log.debug = log.verbose;


var DEFAULT_TIMEOUT= 60000; // 60 s
/**
 * Query a server, using one of the given options
 *
 * @param {Object} opts
 * @param {Array} opts.hosts Array of hosts to query. Until the first success one.
 * @param {Array} opts.path Path to request in each server
 */
var requestList = function(args, cb) {
  $.checkArgument(args.hosts);
  request = args.request || require('request');

import request = require('request');

var $ = require('preconditions').singleton();
const URL = require('url');
const _ = require('lodash');
var Bitcore = require('bitcore-lib');
const Errors = require('./errors');
var Bitcore_ = {
  btc: Bitcore,
  bch: require('bitcore-lib-cash'),
};
// const request = require('request');
const JSON_PAYMENT_REQUEST_CONTENT_TYPE = 'application/payment-request';
const JSON_PAYMENT_VERIFY_CONTENT_TYPE = 'application/verify-payment';
const JSON_PAYMENT_CONTENT_TYPE = 'application/payment';
const JSON_PAYMENT_ACK_CONTENT_TYPE = 'application/payment-ack';

const dfltTrustedKeys = require('../util/JsonPaymentProtocolKeys.js');
const MAX_FEE_PER_KB = 500000;

var $ = require('preconditions').singleton();
var _ = require('lodash');
var log = require('npmlog');

var Bitcore = require('bitcore');
var WalletUtils = require('../walletutils')

/* 
 * Checks data given by the server
 */

function Verifier(opts) {};

Verifier.checkAddress = function(data, address) {
  var local = WalletUtils.deriveAddress(data.publicKeyRing, address.path, data.m, data.network);
  return (local.address == address.address && JSON.stringify(local.publicKeys) == JSON.stringify(address.publicKeys));
};

var _ = require('lodash');
var async = require('async');
var $ = require('preconditions').singleton();

var log = require('npmlog');
log.debug = log.verbose;


var DEFAULT_TIMEOUT= 60000; // 60 s
/**
 * Query a server, using one of the given options
 *
 * @param {Object} opts
 * @param {Array} opts.hosts Array of hosts to query. Until the first success one.
 * @param {Array} opts.path Path to request in each server
 */
var requestList = function(args, cb) {
  $.checkArgument(args.hosts);
  request = args.request || require('request');

'use strict';

var crypto = require('crypto');
var $ = require('preconditions').singleton();
var _ = require('lodash');

var Bitcore = require('bitcore-lib');
var Mnemonic = require('bitcore-mnemonic');
var sjcl = require('sjcl');

var Common = require('./common');
var Constants = Common.Constants;

var FIELDS = [
  'walletId',
  'network',
  'xPrivKey',
  'xPrivKeyEncrypted',
  'xPubKey',
  'publicKeyRing',

var log = require('../util/log');
var networks = require('../networks');
var Address = require('./Address');
var Peer = require('./Peer');
var PeerManager = require('./PeerManager');
var util = require('util');
var EventEmitter = require('events').EventEmitter;
var preconditions = require('preconditions').singleton();

var NetworkMonitor = function(peerman) {
  preconditions.checkArgument(peerman);
  this.peerman = peerman;
  this.networkName = peerman.config.network;
  this.init();
}

util.inherits(NetworkMonitor, EventEmitter);

NetworkMonitor.create = function(config) {
  var peerman = new PeerManager({
    network: config.networkName
  });

  peerman.addPeer(new Peer(config.host, config.port));