Added filterWhere function to FindWrapper

README.md

@@ -166,6 +166,9 @@ Returns a new `FindWrapper` with a subset of the previously selected elements gi
 
 Uses the same possible selectors as [`RenderContext#find(selector)`](#rendercontextfindselector).
 
+### `FindWrapper#filterWhere(predicate)`
+Returns a new `FindWrapper` with a subset of the previously selected elements which, when passed into the provided predicate function, return true.
+
 ### `FindWrapper#find(selector)`
 Selects descendents of the elements previously selected. Returns a new `FindWrapper` with the newly selected elements.
 

index.d.ts

@@ -32,6 +32,12 @@ export interface FindWrapper<P, S> {
      **/
     filter<Q, T>(selector: string): FindWrapper<Q, T>;
 
+    /**
+     * Returns a new `FindWrapper` with a subset of the previously selected elements which, when passed into the
+     * provided predicate function, return true.
+     **/
+    filterWhere<Q, T>(predicate:(element: FindWrapper<Q, T>, index: number) => boolean): FindWrapper<Q, T>;
+
     /**
      * Selects descendents of the elements previously selected. Returns a new `FindWrapper` with the newly selected
      * elements.
@@ -84,4 +90,4 @@ interface ShallowFunction {
 export const deep: DeepFunction;
 export const render: DeepFunction;
 export const shallow: ShallowFunction;
-export default deep;
+export default deep;

src/preact-render-spy.js

@@ -270,6 +270,16 @@ class FindWrapper {
     );
   }
 
+  filterWhere(predicate) {
+    verifyFoundNodes(this);
+    return new FindWrapper(
+      this.context,
+      Array.from(this).filter(
+        (vnode, ...attrs) => predicate(new FindWrapper(this.context, [vnode]), ...attrs)
+      )
+    );
+  }
+
   component() {
     if (this.length !== 1) {
       throw new Error('preact-render-spy: component method can only be used on a single node');

src/shared-render.test.js

@@ -171,6 +171,14 @@ const sharedTests = (name, func) => {
     expect(context.filter(<span />).length).toBe(0);
   });
 
+  it(`${name}: filterWhere() filters components using predicates `, () => {
+    const context = func(<div><NullStateless class="first" /><NullStateless class="second" /></div>);
+    expect(context.find('NullStateless').length).toBe(2);
+    expect(context.find('NullStateless').filterWhere(() => true).length).toBe(2);
+    expect(context.find('NullStateless').filterWhere(() => false).length).toBe(0);
+    expect(context.find('NullStateless').filterWhere(n => n.attr('class') === 'first').length).toBe(1);
+  });
+
   it(`${name}: output returns vdom output by a Component`, () => {
     const context = func(<DivChildren><span /></DivChildren>);
     expect(() => context.find('div').output()).toThrow();