feat(axe.d.ts): add nodeSerializer typings (#4551)

This API was added in pr #4093, but TS definitions were never added.

For simplicity I'm using SerialDqElement in the API. We could introduce
a generic for the custom serialized type (T extends SerialDqElement),
but it's hard to consistently use it everywhere (AxeReporter,
NodeSerializer.dqElmToSpec).

I also fixed DqElement.mergeSpecs which is needed to implement a custom
node serializer: it exists on the constructor and not on the individual
instances

axe.d.ts

@@ -342,6 +342,9 @@ declare namespace axe {
   interface DqElement extends SerialDqElement {
     element: Element;
     toJSON(): SerialDqElement;
+  }
+  interface DqElementConstructor {
+    new (elm: Element, options?: { absolutePaths?: boolean }): DqElement;
     mergeSpecs(
       childSpec: SerialDqElement,
       parentSpec: SerialDqElement
@@ -405,6 +408,24 @@ declare namespace axe {
     boundingClientRect: DOMRect;
   }
 
+  interface CustomNodeSerializer<T = SerialDqElement> {
+    toSpec: (dqElm: DqElement) => T;
+    mergeSpecs: (nodeSpec: T, parentFrameSpec: T) => T;
+  }
+
+  interface NodeSerializer {
+    update: <T>(serializer: CustomNodeSerializer<T>) => void;
+    toSpec: (node: Element | VirtualNode) => SerialDqElement;
+    dqElmToSpec: (
+      dqElm: DqElement | SerialDqElement,
+      options?: RunOptions
+    ) => SerialDqElement;
+    mergeSpecs: (
+      nodeSpec: SerialDqElement,
+      parentFrameSpec: SerialDqElement
+    ) => SerialDqElement;
+  }
+
   interface Utils {
     getFrameContexts: (
       context?: ElementContext,
@@ -423,15 +444,13 @@ declare namespace axe {
       selector: unknown
     ) => selector is LabelledShadowDomSelector;
 
-    DqElement: new (
-      elm: Element,
-      options?: { absolutePaths?: boolean }
-    ) => DqElement;
+    DqElement: DqElementConstructor;
     uuid: (
       options?: { random?: Uint8Array | Array<number> },
       buf?: Uint8Array | Array<number>,
       offset?: number
     ) => string | Uint8Array | Array<number>;
+    nodeSerializer: NodeSerializer;
   }
 
   interface Aria {

typings/axe-core/axe-core-tests.ts

@@ -450,6 +450,19 @@ if (axe.utils.isLabelledShadowDomSelector(unknownContext)) {
 } else if (axe.utils.isContextSpec(unknownContext)) {
   let context: axe.ContextSpec = unknownContext;
 }
+axe.utils.nodeSerializer.update({
+  toSpec(dqElm: axe.DqElement) {
+    return dqElm.toJSON();
+  },
+  mergeSpecs(childSpec: axe.SerialDqElement, parentSpec: axe.SerialDqElement) {
+    return axe.utils.DqElement.mergeSpecs(childSpec, parentSpec);
+  }
+});
+const spec2: axe.SerialDqElement = axe.utils.nodeSerializer.toSpec(element);
+const spec3: axe.SerialDqElement = axe.utils.nodeSerializer.dqElmToSpec(
+  dqElement,
+  options
+);
 
 // Commons
 axe.commons.aria.getRoleType('img');