How to use the gm.subClass function in gm

function analyzeImage(doc, fileName, analyzeCallback) {
    console.log("Starting Analyze Image Method");
    var
    request = require('request'),
    async = require('async'),
    fs = require('fs'),
    gm = require('gm').subClass({
                                imageMagick: true
                                }),
    analysis = {};

    async.parallel([
                    function (callback) {
                    // Write down meta data about the image
                    gm(fileName).size(function (err, size) {
                                      if (err) {
                                      console.log("Image size", err);
                                      } else {
                                      analysis.size = size;
                                      }
                                      callback(null);
                                      });
                    },

let express = require('express'),
    fs      = require('fs'),
    fse     = require('fs-extra'),
    mkdirP  = require('mkdirp'),
    multer  = require('multer'),
    crypto  = require('crypto'),
    mime    = require('mime'),
    path    = require('path'),
    config  = require('../config/config'),
    User    = require('../models/user.model'),
    Form    = require('../models/form.model'),
    gm      = require('gm').subClass({imageMagick: true});

process.on('uncaughtException', (err) => {
  console.log(err);
});

// this function deletes the image
let rmDir = (dirPath, removeSelf) => {
  if (removeSelf === undefined)
    removeSelf = true;
  try {
    var files = fs.readdirSync(dirPath);
  }
  catch (e) {
    return;
  }
  if (files.length > 0)

import fs from 'fs'
import path from 'path'
import gm from 'gm'
import spawn from 'cross-spawn'
import mkdirp from 'mkdirp'
import tmp from 'tmp'

const gmMagick = gm.subClass({ imageMagick: true })

function transparent(filename, options) {
  if (!options.width || !options.height) {
    throw new Error('Wrong options provided to transparent()')
  }

  const gmImage = gmMagick(filename)
  gmImage.background('transparent') // Fill in new space with white background
  gmImage.gravity('NorthWest') // Anchor image to upper-left
  gmImage.extent(options.width, options.height) // Specify new image size

  return gmImage
}

function getImageSize(filename) {
  return new Promise((accept, reject) => {

// image operation.

var
    fs = require('fs'),
    gm = require('gm').subClass({ imageMagick : true });

function calcScaleSize(origin_width, origin_height, resize_width, resize_height, keepAspect) {
    function isEnlarge(tw, th) {
        return origin_width < tw && origin_height < th;
    }

    if (resize_width <= 0 && resize_height <= 0) {
        throw {"name": "Parameter error!"};
    }
    if (keepAspect === undefined) {
        keepAspect = true;
    }
    if (origin_width === resize_width && origin_height === resize_height) {
        return { width: origin_width, height: origin_height, resized: false, enlarge: false };
    }
    var

const farmhash = require("farmhash");
const imageinfo = require("imageinfo");
let gm = require("gm");
const async = require("async");

const models = require("../lib/models");
const urls = require("../lib/urls");
const db = require("../lib/db");
const similar = require("../lib/similar");
const config = require("../lib/config");

// Add the ability to provide an explicit bath to the GM binary
/* istanbul ignore if */
if (config.GM_PATH) {
    gm = gm.subClass({appPath: config.GM_PATH});
}

const Image = new db.schema({
    // An ID for the image in the form: SOURCE/IMAGENAME
    _id: String,

    // The date that this item was created
    created: {
        type: Date,
        default: Date.now,
    },

    // The date that this item was updated
    modified: {
        type: Date,
    },

'use strict';

const gm = require('gm').subClass({imageMagick: true});
const _ = require('lodash');
const fs = require('fs');
const os = require('os');
const mkdirp = require('mkdirp');
const child_process = require('child_process');
const async = require('async');


let OUT_DIR = os.tmpDir() + '/app-icon/output';

const androidIconSize = {
  // 'web': { w: 512, h: 512 },
  'ldpi': { w: 36, h: 36 },
  'mdpi': { w: 48, h: 48 },
  'hdpi': { w: 72, h: 72 },
  'xhdpi': { w: 96, h: 96 },

var express = require('express'),
  router = express.Router(),
  passwordHash = require('password-hash'),
  jwt = require('jsonwebtoken'),
  config = require('../config/config'),
  fs = require('fs'),
  multer = require('multer'),
  mime = require('mime'),
  path = require('path'),
  crypto = require("crypto"),
  gm = require('gm').subClass({imageMagick: true});

var User = require('../models/user.model');

// user register
router.post('/register', function (req, res, next) {
  var user = new User({
    email: req.body.email,
    password: passwordHash.generate(req.body.password)
  });
  user.save(function (err, result) {
    if (err) {
      return res.status(403).json({
        title: 'There was an issue',
        error: {message: 'The email you entered already exists'}
      });
    }

'use strict';

/**
 * image operation.
 * 
 * ImageMagick MUST be installed first.
 * 
 * author: Michael Liao
 */

const
    bluebird = require('bluebird'),
    api = require('./api'),
    logger = require('./logger'),
    gm = require('gm').subClass({ imageMagick : true });

function calcScaleSize(origin_width, origin_height, resize_width, resize_height, keepAspect) {
    function isEnlarge(tw, th) {
        return origin_width < tw && origin_height < th;
    }

    if (resize_width <= 0 && resize_height <= 0) {
        throw new Error('invalid parameter: ' + resize_width + ', ' + resize_height);
    }
    if (keepAspect === undefined) {
        keepAspect = true;
    }
    if (origin_width === resize_width && origin_height === resize_height) {
        return { width: origin_width, height: origin_height, resized: false, enlarge: false };
    }
    let

let express     = require('express'),
    User        = require('../models/user.model'),
    jwt         = require('jsonwebtoken'),
    config      = require('../config/config'),
    fs          = require('fs'),
    multer      = require('multer'),
    mime        = require('mime'),
    path        = require('path'),
    crypto      = require('crypto'),
    gm          = require('gm').subClass({imageMagick: true}),
    nodemailer  = require('nodemailer'),
    hbs         = require('nodemailer-express-handlebars'),
    sgTransport = require('nodemailer-sendgrid-transport'),
    uuidV1      = require('uuid/v1'),
    async       = require('async');

function generateToken(user) {
  return jwt.sign(user, config.secret, {expiresIn: config.jwtExpire});
}

function setUserInfo(req) {
  return {
    _id  : req._id,
    email: req.email,
    role : req.role
  };

"use strict";

var multer = require("multer");
var fs = require("fs");
var gm = require("gm").subClass({ imageMagick: true });
var path = require("path");


var imagePath = "./server/static/images/";
var upload = multer({ dest: imagePath });

/**
 * Creating directory for specific image size if not exists
 * requires npm "fs" module.
 */
function createDirIfNotExists(path){
    if (!fs.existsSync(path)){
        fs.mkdirSync(path);
    }
}