Stringfy object functions in javascript https://jsfiddle.net/p24b9f8n/38/

stringfy.js

var stringify = function(obj, prop) {
  var placeholder = '____PLACEHOLDER____';
  var fns = [];
  var json = JSON.stringify(obj, function(key, value) {
    if (typeof value === 'function') {
      fns.push(value);
      return placeholder;
    }
    return value;
  }, 2);
  json = json.replace(new RegExp('"' + placeholder + '"', 'g'), function(_) {
    return fns.shift();
  });
  return 'var ' + prop + ' = ' + json + ';';
};

var rides = {
  brand: {
    type: "String",
    label: "搜尋",
    max: "100"
  },
  model: {
    type: "String",
    label: "Tìm kiếm",
    max: "100"
  },
  fueltype: {
    type: "String",
    label: "Пошук",
    allowedValues: ['Petrol', 'Diesel', 'Hybrid', 'Electric'],
  },
  bodystyle: {
    type: "String",
    label: "بحث",
    allowedValues: ['Convertibles', 'Coupes', 'Hatchbacks', 'Vans', 'Sedans', 'Suvs', 'Trucks', 'Wagons'],
    optional: "true"
  },
  topspeed: {
    type: "Number",
    label: "חיפוש",
    optional: "true"
  },
  power: {
    type: "Number",
    label: "Power (HP)",
    optional: "true"
  }
};

var processed = stringify(rides,'rides');
var find = '"type": "String"';
var find_number = '"type": "Number"';
var find_boolean_true = '"optional": "true"';
var find_boolean_false = '"optional": "false"';
var find_max = '"max": "100"';
var re = new RegExp(find, 'g');
var re_number = new RegExp(find_number, 'g');
var re_boolean_true = new RegExp(find_boolean_true, 'g');
var re_boolean_false = new RegExp(find_boolean_false, 'g');
var re_max = new RegExp(find_max, 'g');

var processed = processed.replace(re, '"type": String');
var processed = processed.replace(re_number, '"type": Number');
var processed = processed.replace(re_boolean_true, '"optional": true');
var processed = processed.replace(re_boolean_false, '"optional": false');
var processed = processed.replace(re_max, '"max": 100');


console.log(processed);