fix(): Fix broken exports for filters that do not have a static defaults value.

CHANGELOG.md

@@ -2,6 +2,7 @@
 
 ## [next]
 
+- fix(): Fix broken exports for filters that do not have a static defaults value. [#10102](https://github.com/fabricjs/fabric.js/pull/10102)
 - chore(): deprecate originX, originY [#10095](https://github.com/fabricjs/fabric.js/pull/10095)
 - fix(SVGImport): Allow parsing of 'id' attribute that starts with a number [#10079](https://github.com/fabricjs/fabric.js/pull/10079)
 - fix(filter): pixelate filter has non square pixels in webgl (#10081)

src/filters/BaseFilter.spec.ts

@@ -0,0 +1,14 @@
+import { BaseFilter } from './BaseFilter';
+
+class SimpleFilter extends BaseFilter<'?'> {
+  static type = '?';
+  declare property: string;
+}
+
+describe('Extended filters', () => {
+  it('can export', () => {
+    const f = new SimpleFilter();
+    const serialized = f.toObject();
+    expect(serialized).toEqual({ type: '?' });
+  });
+});

src/filters/BaseFilter.ts

@@ -377,11 +377,13 @@ export class BaseFilter<
 
   /**
    * Returns object representation of an instance
+   * It will automatically export the default values of a filter,
+   * stored in the static defaults property.
    * @return {Object} Object representation of an instance
    */
   toObject(): { type: Name } & OwnProps {
     const defaultKeys = Object.keys(
-      (this.constructor as typeof BaseFilter).defaults,
+      (this.constructor as typeof BaseFilter).defaults || {},
     ) as (keyof OwnProps)[];
 
     return {