chore: handle default values in formEngine

package.json

@@ -7,7 +7,7 @@
         "dev": "node esbuild.config.mjs",
         "build": "npm run check && node esbuild.config.mjs production",
         "check": "svelte-check --tsconfig tsconfig.json",
-        "test": "jest",
+        "test": "jest --detectOpenHandles",
         "test-w": "jest --watch --no-cache",
         "version": "node version-bump.mjs && git add manifest.json versions.json"
     },

src/store/formStore.test.ts

@@ -85,4 +85,47 @@ describe("Form Engine", () => {
         // Assert that the onSubmit callback is called
         expect(onSubmitMock).toHaveBeenCalledWith({ fieldName1: "value" });
     });
+
+    it("should use default values when field has not been changed, but if they change it should use the value", () => {
+        const onSubmitMock = jest.fn();
+        const defaultValues = {
+            fieldName1: "default1",
+            fieldName2: "default2",
+        };
+        const formEngine = makeFormEngine(onSubmitMock, defaultValues);
+
+        // Add fields to the form
+        const field1 = formEngine.addField({ name: "fieldName1" });
+        const field2 = formEngine.addField({ name: "fieldName2" });
+
+        // Assert that the default values are set
+        expect(get(field1.value)).toBe("default1");
+        expect(get(field2.value)).toBe("default2");
+        field1.value.set("value1");
+        formEngine.triggerSubmit();
+        // Assert that the onSubmit callback is called with the correct values
+        expect(onSubmitMock).toHaveBeenCalledWith({
+            fieldName1: "value1",
+            fieldName2: "default2",
+        });
+    });
+    it("empty values that have not been modified should not be in the result", () => {
+        const onSubmitMock = jest.fn();
+        const defaultValues = {
+            fieldName1: "default1",
+        };
+        const formEngine = makeFormEngine(onSubmitMock, defaultValues);
+
+        // Add fields to the form
+        const field1 = formEngine.addField({ name: "fieldName1" });
+        const field2 = formEngine.addField({ name: "fieldName2" });
+
+        // Assert that the default values are set
+        expect(get(field1.value)).toBe("default1");
+        formEngine.triggerSubmit();
+        // Assert that the onSubmit callback is called with the correct values
+        expect(onSubmitMock).toHaveBeenCalledWith({
+            fieldName1: "default1",
+        });
+    });
 });

src/store/formStore.ts

@@ -142,6 +142,7 @@ export type OnFormSubmit<T> = (values: Record<string, T>) => void;
 
 export function makeFormEngine<T extends FieldValue>(
     onSubmit: OnFormSubmit<T>,
+    defaultValues: Record<string, T> = {},
 ): FormEngine<T> {
     const formStore: Writable<FormStore<T>> = writable({ fields: {} });
     // Creates helper functions to modify the store immutably
@@ -153,7 +154,7 @@ export function makeFormEngine<T extends FieldValue>(
                     ...form,
                     fields: {
                         ...form.fields,
-                        [name]: { value: O.none, name, errors, rules },
+                        [name]: { value: O.fromNullable(defaultValues[name]), name, errors, rules },
                     },
                 };
             });