Add a default validate method on Model

src/model.js

@@ -51,8 +51,6 @@ class Model extends EventEmitter(Object) {
     // The value returned during the last failed validation.
     this.validationError = null;
 
-    this.validate = this.validate ?? null;
-
     if (options.collection) this.collection = options.collection;
     if (options.parse) attrs = this.parse(attrs, options) || {};
 
@@ -114,6 +112,15 @@ class Model extends EventEmitter(Object) {
   // eslint-disable-next-line class-methods-use-this
   initialize() {}
 
+  /**
+   * @param {object} attrs
+   * @param {object} [options]
+   * @returns {string} The validation error message
+   */
+  validate(attrs, options) {
+    return '';
+  }
+
   /**
    * Return a copy of the model's `attributes` object.
    */

src/types/model.d.ts

@@ -65,8 +65,7 @@ export class Model extends Model_base {
     constructor(attributes?: Attributes, options?: ModelOptions, ...args: any[]);
     cid: any;
     attributes: {};
-    validationError: any;
-    validate: any;
+    validationError: string;
     collection: any;
     changed: {};
     /**
@@ -99,6 +98,12 @@ export class Model extends Model_base {
      * initialization logic.
      */
     initialize(): void;
+    /**
+     * @param {object} attrs
+     * @param {object} [options]
+     * @returns {string} The validation error message
+     */
+    validate(attrs: object, options?: object): string;
     /**
      * Return a copy of the model's `attributes` object.
      */