Fix form property assignment edge case (go-gitea#35073)

"form" has an edge case: its `<input name=action>` element overwrites
the `action` property, we can only set attribute.

This PR makes `assignElementProperty` can handle such case, and add more
tests

Author: wxiaoguang

web_src/js/features/common-button.test.ts

@@ -1,12 +1,23 @@
-import {assignElementProperty} from './common-button.ts';
+import {assignElementProperty, type ElementWithAssignableProperties} from './common-button.ts';
 
 test('assignElementProperty', () => {
   const elForm = document.createElement('form');
   assignElementProperty(elForm, 'action', '/test-link');
   expect(elForm.action).contains('/test-link'); // the DOM always returns absolute URL
+  expect(elForm.getAttribute('action')).eq('/test-link');
   assignElementProperty(elForm, 'text-content', 'dummy');
   expect(elForm.textContent).toBe('dummy');
 
+  // mock a form with its property "action" overwritten by an input element
+  const elFormWithAction = new class implements ElementWithAssignableProperties {
+    action = document.createElement('input'); // now "form.action" is not string, but an input element
+    _attrs: Record<string, string> = {};
+    setAttribute(name: string, value: string) { this._attrs[name] = value }
+    getAttribute(name: string): string | null { return this._attrs[name] }
+  }();
+  assignElementProperty(elFormWithAction, 'action', '/bar');
+  expect(elFormWithAction.getAttribute('action')).eq('/bar');
+
   const elInput = document.createElement('input');
   expect(elInput.readOnly).toBe(false);
   assignElementProperty(elInput, 'read-only', 'true');

web_src/js/features/common-button.ts

@@ -102,18 +102,26 @@ function onHidePanelClick(el: HTMLElement, e: MouseEvent) {
   throw new Error('no panel to hide'); // should never happen, otherwise there is a bug in code
 }
 
-export function assignElementProperty(el: any, name: string, val: string) {
-  name = camelize(name);
-  const old = el[name];
+export type ElementWithAssignableProperties = {
+  getAttribute: (name: string) => string | null;
+  setAttribute: (name: string, value: string) => void;
+} & Record<string, any>
+
+export function assignElementProperty(el: ElementWithAssignableProperties, kebabName: string, val: string) {
+  const camelizedName = camelize(kebabName);
+  const old = el[camelizedName];
   if (typeof old === 'boolean') {
-    el[name] = val === 'true';
+    el[camelizedName] = val === 'true';
   } else if (typeof old === 'number') {
-    el[name] = parseFloat(val);
+    el[camelizedName] = parseFloat(val);
   } else if (typeof old === 'string') {
-    el[name] = val;
+    el[camelizedName] = val;
+  } else if (old?.nodeName) {
+    // "form" has an edge case: its "<input name=action>" element overwrites the "action" property, we can only set attribute
+    el.setAttribute(kebabName, val);
   } else {
     // in the future, we could introduce a better typing system like `data-modal-form.action:string="..."`
-    throw new Error(`cannot assign element property ${name} by value ${val}`);
+    throw new Error(`cannot assign element property "${camelizedName}" by value "${val}"`);
   }
 }