Rename `isDocumentReady` to `onDocumentReady`

The name of `isDocumentReady` gives the impressiong that the function
would return a boolean.  `onDocumentReady`, on the other hand, expresses
more clearly that the execution of the callback will be triggered after
the iframe's documen is ready (loaded and parsed).

On a follow up commit I change the `onDocumentReady` to return a Promise
instead of executing a callback.

src/annotator/frame-observer.js

@@ -40,7 +40,7 @@ export default class FrameObserver {
    */
   _addFrame(frame) {
     if (isAccessible(frame)) {
-      isDocumentReady(frame, () => {
+      onDocumentReady(frame, () => {
         const frameWindow = /** @type {Window} */ (frame.contentWindow);
         frameWindow.addEventListener('unload', () => {
           this._removeFrame(frame);
@@ -92,10 +92,12 @@ function isAccessible(iframe) {
 }
 
 /**
+ * Triggers a callback when the iframe's DOM is ready (loaded and parsed)
+ *
  * @param {HTMLIFrameElement} iframe
  * @param {() => void} callback
  */
-export function isDocumentReady(iframe, callback) {
+export function onDocumentReady(iframe, callback) {
   const iframeDocument = /** @type {Document} */ (iframe.contentDocument);
   if (iframeDocument.readyState === 'loading') {
     iframeDocument.addEventListener('DOMContentLoaded', () => {

src/annotator/test/integration/hypothesis-injector-test.js

 import { DEBOUNCE_WAIT } from '../../frame-observer';
 import { HypothesisInjector } from '../../hypothesis-injector';
-import { isDocumentReady } from '../../frame-observer';
+import { onDocumentReady } from '../../frame-observer';
 
 describe('HypothesisInjector integration test', () => {
   let container;
@@ -65,7 +65,7 @@ describe('HypothesisInjector integration test', () => {
     createHypothesisInjector();
 
     const validFramePromise = new Promise(resolve => {
-      isDocumentReady(validFrame, () => {
+      onDocumentReady(validFrame, () => {
         assert(
           validFrame.contentDocument.body.hasChildNodes(),
           'expected valid frame to be modified'
@@ -74,7 +74,7 @@ describe('HypothesisInjector integration test', () => {
       });
     });
     const invalidFramePromise = new Promise(resolve => {
-      isDocumentReady(invalidFrame, () => {
+      onDocumentReady(invalidFrame, () => {
         assert(
           !invalidFrame.contentDocument.body.hasChildNodes(),
           'expected invalid frame to not be modified'
@@ -105,7 +105,7 @@ describe('HypothesisInjector integration test', () => {
     createHypothesisInjector();
 
     return new Promise(resolve => {
-      isDocumentReady(frame, () => {
+      onDocumentReady(frame, () => {
         const scriptElement =
           frame.contentDocument.querySelector('script[src]');
         assert(scriptElement, 'expected embed script to be injected');
@@ -128,7 +128,7 @@ describe('HypothesisInjector integration test', () => {
     createHypothesisInjector();
 
     return new Promise(resolve => {
-      isDocumentReady(frame, () => {
+      onDocumentReady(frame, () => {
         const scriptElement =
           frame.contentDocument.querySelector('script[src]');
         assert.isNull(
@@ -150,7 +150,7 @@ describe('HypothesisInjector integration test', () => {
     return new Promise(resolve => {
       // Yield to let the DOM and CrossFrame catch up
       waitForFrameObserver(() => {
-        isDocumentReady(frame, () => {
+        onDocumentReady(frame, () => {
           assert(
             frame.contentDocument.body.hasChildNodes(),
             'expected dynamically added frame to be modified'
@@ -192,7 +192,7 @@ describe('HypothesisInjector integration test', () => {
     createHypothesisInjector();
 
     return new Promise(resolve => {
-      isDocumentReady(frame, () => {
+      onDocumentReady(frame, () => {
         assert(
           frame.contentDocument.body.hasChildNodes(),
           'expected initial frame to be modified'
@@ -207,7 +207,7 @@ describe('HypothesisInjector integration test', () => {
 
           // Yield again
           waitForFrameObserver(() => {
-            isDocumentReady(frame, () => {
+            onDocumentReady(frame, () => {
               assert(
                 frame.contentDocument.body.hasChildNodes(),
                 'expected dynamically added frame to be modified'
@@ -230,7 +230,7 @@ describe('HypothesisInjector integration test', () => {
     return new Promise(resolve => {
       // Yield to let the DOM and CrossFrame catch up
       waitForFrameObserver(() => {
-        isDocumentReady(frame, () => {
+        onDocumentReady(frame, () => {
           assert(
             frame.contentDocument.body.hasChildNodes(),
             'expected dynamically added frame to be modified'
@@ -245,7 +245,7 @@ describe('HypothesisInjector integration test', () => {
 
             // Yield
             waitForFrameObserver(() => {
-              isDocumentReady(frame, () => {
+              onDocumentReady(frame, () => {
                 assert(
                   frame.contentDocument.body.hasChildNodes(),
                   'expected dynamically added frame to be modified'