perf: some more micro optimizations for find() and findOne() re: #14906

Author: vkarpov15

lib/document.js

@@ -741,15 +741,10 @@ function init(self, obj, doc, opts, prefix) {
   let schemaType;
   let path;
   let i;
-  let index = 0;
   const strict = self.$__.strictMode;
   const docSchema = self.$__schema;
 
-  while (index < len) {
-    _init(index++);
-  }
-
-  function _init(index) {
+  for (let index = 0; index < len; ++index) {
     i = keys[index];
     // avoid prototype pollution
     if (i === '__proto__' || i === 'constructor') {

lib/query.js

@@ -65,6 +65,22 @@ const queryOptionMethods = new Set([
   'wtimeout'
 ]);
 
+const opToThunk = new Map([
+  ['countDocuments', '_countDocuments'],
+  ['distinct', '__distinct'],
+  ['estimatedDocumentCount', '_estimatedDocumentCount'],
+  ['find', '_find'],
+  ['findOne', '_findOne'],
+  ['findOneAndReplace', '_findOneAndReplace'],
+  ['findOneAndUpdate', '_findOneAndUpdate'],
+  ['replaceOne', '_replaceOne'],
+  ['updateMany', '_updateMany'],
+  ['updateOne', '_updateOne'],
+  ['deleteMany', '_deleteMany'],
+  ['deleteOne', '_deleteOne'],
+  ['findOneAndDelete', '_findOneAndDelete']
+]);
+
 /**
  * Query constructor used for building queries. You do not need
  * to instantiate a `Query` directly. Instead use Model functions like
@@ -4397,22 +4413,14 @@ Query.prototype.exec = async function exec(op) {
   if (this.model == null) {
     throw new MongooseError('Query must have an associated model before executing');
   }
-  this._validateOp();
-
-  if (!this.op) {
-    return;
-  }
 
-  if (this.options && this.options.sort) {
-    const keys = Object.keys(this.options.sort);
-    if (keys.includes('')) {
-      throw new Error('Invalid field "" passed to sort()');
-    }
+  const thunk = opToThunk.get(this.op);
+  if (!thunk) {
+    throw new MongooseError('Query has invalid `op`: "' + this.op + '"');
   }
 
-  let thunk = '_' + this.op;
-  if (this.op === 'distinct') {
-    thunk = '__distinct';
+  if (this.options && this.options.sort && typeof this.options.sort === 'object' && this.options.sort.hasOwnProperty('')) {
+    throw new Error('Invalid field "" passed to sort()');
   }
 
   if (this._executionStack != null) {