perf(document+internal): put default value for $isNew and `strictMo…

…de` on prototype to avoid unnecessary memory usage

Re: #11541

lib/document.js

@@ -93,7 +93,11 @@ function Document(obj, fields, skipId, options) {
   }
 
   this.$__ = new InternalCache();
-  this.$isNew = 'isNew' in options ? options.isNew : true;
+
+  // Avoid setting `isNew` to `true`, because it is `true` by default
+  if (options.isNew != null && options.isNew !== true) {
+    this.$isNew = options.isNew;
+  }
 
   if (options.priorDoc != null) {
     this.$__.priorDoc = options.priorDoc;
@@ -116,9 +120,11 @@ function Document(obj, fields, skipId, options) {
   const schema = this.$__schema;
 
   if (typeof fields === 'boolean' || fields === 'throw') {
-    this.$__.strictMode = fields;
+    if (fields !== true) {
+      this.$__.strictMode = fields;
+    }
     fields = undefined;
-  } else {
+  } else if (schema.options.strict !== true) {
     this.$__.strictMode = schema.options.strict;
   }
 
@@ -207,6 +213,13 @@ Object.defineProperty(Document.prototype, 'errors', {
     this.$errors = value;
   }
 });
+
+/*!
+ * ignore
+ */
+
+Document.prototype.$isNew = true;
+
 /*!
  * Document exposes the NodeJS event emitter API, so you can use
  * `on`, `once`, etc.

lib/internal.js

@@ -13,8 +13,9 @@ function InternalCache() {
   this.activePaths = new ActiveRoster();
 }
 
+InternalCache.prototype.strictMode = true;
+
 InternalCache.prototype.fullPath = undefined;
-InternalCache.prototype.strictMode = undefined;
 InternalCache.prototype.selected = undefined;
 InternalCache.prototype.shardval = undefined;
 InternalCache.prototype.saveError = undefined;