Use faster implementation for merging

lib/Onyx.js

@@ -7,6 +7,7 @@ import * as Logger from './Logger';
 import cache from './OnyxCache';
 import createDeferredTask from './createDeferredTask';
 import mergeWithCustomized from './mergeWithCustomized';
+import { merge } from './fastMerge';
 
 // Keeps track of the last connectionID that was used so we can keep incrementing it
 let lastConnectionID = 0;
@@ -761,7 +762,7 @@ function applyMerge(key, data) {
     if (_.isObject(data) || _.every(mergeValues, _.isObject)) {
         // Object values are merged one after the other
         return _.reduce(mergeValues, (modifiedData, mergeValue) => {
-            const newData = mergeWithCustomized({}, modifiedData, mergeValue);
+            const newData = Object.assign({}, merge(modifiedData, mergeValue));
 
             // We will also delete any object keys that are undefined or null.
             // Deleting keys is not supported by AsyncStorage so we do it this way.

lib/OnyxCache.js

@@ -1,5 +1,6 @@
 import _ from 'underscore';
 import mergeWithCustomized from './mergeWithCustomized';
+import { merge } from './fastMerge';
 
 const isDefined = _.negate(_.isUndefined);
 
@@ -110,7 +111,7 @@ class OnyxCache {
      * @param {Record<string, *>} data - a map of (cache) key - values
      */
     merge(data) {
-        this.storageMap = mergeWithCustomized({}, this.storageMap, data);
+        this.storageMap = Object.assign({}, merge(this.storageMap, data));
 
         const storageKeys = this.getAllKeys();
         const mergedKeys = _.keys(data);

lib/fastMerge.js

@@ -0,0 +1,40 @@
+// Mostly copied from  https://medium.com/@lubaka.a/how-to-remove-lodash-performance-improvement-b306669ad0e1
+
+function isMergeableObject(val) {
+  var nonNullObject = val && typeof val === 'object';
+  return nonNullObject &&
+    Object.prototype.toString.call(val) !== '[object RegExp]' &&
+    Object.prototype.toString.call(val) !== '[object Date]';
+}
+
+let key = "";
+function mergeObject(target, source) {
+  var destination = {};
+  if (isMergeableObject(target)) {
+    const targetKeys = Object.keys(target);
+    for (let i = 0; i < targetKeys.length; ++i) {
+      key = targetKeys[i];
+      destination[key] = target[key];
+    }
+  }
+  const sourceKeys = Object.keys(source);
+  for (let i = 0; i < sourceKeys.length; ++i) {
+    const key = sourceKeys[i];
+    if (!isMergeableObject(source[key]) || !target[key]) {
+      destination[key] = source[key];
+    } else {
+      destination[key] = merge(target[key], source[key])
+    }
+  }
+
+  return destination;
+}
+
+export function merge(target, source) {
+  var array = Array.isArray(source);
+  if (array) {
+    return source;
+  } else {
+    return mergeObject(target, source);
+  }
+}