some progress

node_modules/mongoose/lib/helpers/clone.js

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+'use strict';
+
+const Decimal = require('../types/decimal128');
+const ObjectId = require('../types/objectid');
+const specialProperties = require('./specialProperties');
+const isMongooseObject = require('./isMongooseObject');
+const getFunctionName = require('./getFunctionName');
+const isBsonType = require('./isBsonType');
+const isMongooseArray = require('../types/array/isMongooseArray').isMongooseArray;
+const isObject = require('./isObject');
+const isPOJO = require('./isPOJO');
+const symbols = require('./symbols');
+const trustedSymbol = require('./query/trusted').trustedSymbol;
+
+/**
+ * Object clone with Mongoose natives support.
+ *
+ * If options.minimize is true, creates a minimal data object. Empty objects and undefined values will not be cloned. This makes the data payload sent to MongoDB as small as possible.
+ *
+ * Functions are never cloned.
+ *
+ * @param {Object} obj the object to clone
+ * @param {Object} options
+ * @param {Boolean} isArrayChild true if cloning immediately underneath an array. Special case for minimize.
+ * @return {Object} the cloned object
+ * @api private
+ */
+
+function clone(obj, options, isArrayChild) {
+  if (obj == null) {
+    return obj;
+  }
+
+  if (Array.isArray(obj)) {
+    return cloneArray(isMongooseArray(obj) ? obj.__array : obj, options);
+  }
+
+  if (isMongooseObject(obj)) {
+    // Single nested subdocs should apply getters later in `applyGetters()`
+    // when calling `toObject()`. See gh-7442, gh-8295
+    if (options && options._skipSingleNestedGetters && obj.$isSingleNested) {
+      options = Object.assign({}, options, { getters: false });
+    }
+    const isSingleNested = obj.$isSingleNested;
+
+    if (isPOJO(obj) && obj.$__ != null && obj._doc != null) {
+      return obj._doc;
+    }
+
+    let ret;
+    if (options && options.json && typeof obj.toJSON === 'function') {
+      ret = obj.toJSON(options);
+    } else {
+      ret = obj.toObject(options);
+    }
+
+    if (options && options.minimize && isSingleNested && Object.keys(ret).length === 0) {
+      return undefined;
+    }
+
+    return ret;
+  }
+
+  const objConstructor = obj.constructor;
+
+  if (objConstructor) {
+    switch (getFunctionName(objConstructor)) {
+      case 'Object':
+        return cloneObject(obj, options, isArrayChild);
+      case 'Date':
+        return new objConstructor(+obj);
+      case 'RegExp':
+        return cloneRegExp(obj);
+      default:
+        // ignore
+        break;
+    }
+  }
+
+  if (isBsonType(obj, 'ObjectId')) {
+    return new ObjectId(obj.id);
+  }
+
+  if (isBsonType(obj, 'Decimal128')) {
+    if (options && options.flattenDecimals) {
+      return obj.toJSON();
+    }
+    return Decimal.fromString(obj.toString());
+  }
+
+  // object created with Object.create(null)
+  if (!objConstructor && isObject(obj)) {
+    return cloneObject(obj, options, isArrayChild);
+  }
+
+  if (typeof obj === 'object' && obj[symbols.schemaTypeSymbol]) {
+    return obj.clone();
+  }
+
+  // If we're cloning this object to go into a MongoDB command,
+  // and there's a `toBSON()` function, assume this object will be
+  // stored as a primitive in MongoDB and doesn't need to be cloned.
+  if (options && options.bson && typeof obj.toBSON === 'function') {
+    return obj;
+  }
+
+  if (typeof obj.valueOf === 'function') {
+    return obj.valueOf();
+  }
+
+  return cloneObject(obj, options, isArrayChild);
+}
+module.exports = clone;
+
+/*!
+ * ignore
+ */
+
+function cloneObject(obj, options, isArrayChild) {
+  const minimize = options && options.minimize;
+  const omitUndefined = options && options.omitUndefined;
+  const seen = options && options._seen;
+  const ret = {};
+  let hasKeys;
+
+  if (seen && seen.has(obj)) {
+    return seen.get(obj);
+  } else if (seen) {
+    seen.set(obj, ret);
+  }
+  if (trustedSymbol in obj) {
+    ret[trustedSymbol] = obj[trustedSymbol];
+  }
+
+  let i = 0;
+  let key = '';
+  const keys = Object.keys(obj);
+  const len = keys.length;
+
+  for (i = 0; i < len; ++i) {
+    if (specialProperties.has(key = keys[i])) {
+      continue;
+    }
+
+    // Don't pass `isArrayChild` down
+    const val = clone(obj[key], options, false);
+
+    if ((minimize === false || omitUndefined) && typeof val === 'undefined') {
+      delete ret[key];
+    } else if (minimize !== true || (typeof val !== 'undefined')) {
+      hasKeys || (hasKeys = true);
+      ret[key] = val;
+    }
+  }
+
+  return minimize && !isArrayChild ? hasKeys && ret : ret;
+}
+
+function cloneArray(arr, options) {
+  let i = 0;
+  const len = arr.length;
+  const ret = new Array(len);
+  for (i = 0; i < len; ++i) {
+    ret[i] = clone(arr[i], options, true);
+  }
+
+  return ret;
+}
+
+function cloneRegExp(regexp) {
+  const ret = new RegExp(regexp.source, regexp.flags);
+
+  if (ret.lastIndex !== regexp.lastIndex) {
+    ret.lastIndex = regexp.lastIndex;
+  }
+  return ret;
+}