1 files changed, 25 insertions, 8 deletions

diff --git a/ext/js/dom/text-source-range.js b/ext/js/dom/text-source-range.js
index d5e70052..5c3d4184 100644
--- a/ext/js/dom/text-source-range.js
+++ b/ext/js/dom/text-source-range.js
@@ -36,26 +36,33 @@ export class TextSourceRange {
      * @param {?Element} imposterElement The temporary imposter element.
      * @param {?Element} imposterSourceElement The source element which the imposter is imitating.
      *   Must not be `null` if imposterElement is specified.
-     * @param {?Rect[]} cachedRects A set of cached `DOMRect`s representing the rects of the text source,
+     * @param {?DOMRect[]} cachedRects A set of cached `DOMRect`s representing the rects of the text source,
      *   which can be used after the imposter element is removed from the page.
      *   Must not be `null` if imposterElement is specified.
-     * @param {?Rect} cachedSourceRect A cached `DOMRect` representing the rect of the `imposterSourceElement`,
+     * @param {?DOMRect} cachedSourceRect A cached `DOMRect` representing the rect of the `imposterSourceElement`,
      *   which can be used after the imposter element is removed from the page.
      *   Must not be `null` if imposterElement is specified.
      */
     constructor(range, rangeStartOffset, content, imposterElement, imposterSourceElement, cachedRects, cachedSourceRect) {
+        /** @type {Range} */
         this._range = range;
+        /** @type {number} */
         this._rangeStartOffset = rangeStartOffset;
+        /** @type {string} */
         this._content = content;
+        /** @type {?Element} */
         this._imposterElement = imposterElement;
+        /** @type {?Element} */
         this._imposterSourceElement = imposterSourceElement;
+        /** @type {?DOMRect[]} */
         this._cachedRects = cachedRects;
+        /** @type {?DOMRect} */
         this._cachedSourceRect = cachedSourceRect;
     }
 
     /**
      * Gets the type name of this instance.
-     * @type {string}
+     * @type {'range'}
      */
     get type() {
         return 'range';
@@ -71,7 +78,7 @@ export class TextSourceRange {
 
     /**
      * The starting offset for the range.
-     * @type {Range}
+     * @type {number}
      */
     get rangeStartOffset() {
         return this._rangeStartOffset;
@@ -169,12 +176,12 @@ export class TextSourceRange {
     /**
      * Gets writing mode that is used for this element.
      * See: https://developer.mozilla.org/en-US/docs/Web/CSS/writing-mode.
-     * @returns {string} The rects.
+     * @returns {import('document-util').NormalizedWritingMode} The writing mode.
      */
     getWritingMode() {
         let node = this._isImposterDisconnected() ? this._imposterSourceElement : this._range.startContainer;
         if (node !== null && node.nodeType !== Node.ELEMENT_NODE) { node = node.parentElement; }
-        return DocumentUtil.getElementWritingMode(node);
+        return DocumentUtil.getElementWritingMode(/** @type {?Element} */ (node));
     }
 
     /**
@@ -183,6 +190,7 @@ export class TextSourceRange {
     select() {
         if (this._imposterElement !== null) { return; }
         const selection = window.getSelection();
+        if (selection === null) { return; }
         selection.removeAllRanges();
         selection.addRange(this._range);
     }
@@ -193,6 +201,7 @@ export class TextSourceRange {
     deselect() {
         if (this._imposterElement !== null) { return; }
         const selection = window.getSelection();
+        if (selection === null) { return; }
         selection.removeAllRanges();
     }
 
@@ -220,7 +229,7 @@ export class TextSourceRange {
             try {
                 return this._range.compareBoundaryPoints(Range.START_TO_START, other.range) === 0;
             } catch (e) {
-                if (e.name === 'WrongDocumentError') {
+                if (e instanceof Error && e.name === 'WrongDocumentError') {
                     // This can happen with shadow DOMs if the ranges are in different documents.
                     return false;
                 }
@@ -269,9 +278,17 @@ export class TextSourceRange {
 
     /**
      * Gets the cached rects for a disconnected imposter element.
-     * @returns {Rect[]} The rects for the element.
+     * @returns {DOMRect[]} The rects for the element.
+     * @throws {Error}
      */
     _getCachedRects() {
+        if (
+            this._cachedRects === null ||
+            this._cachedSourceRect === null ||
+            this._imposterSourceElement === null
+        ) {
+            throw new Error('Cached rects not valid for this instance');
+        }
         const sourceRect = DocumentUtil.convertRectZoomCoordinates(this._imposterSourceElement.getBoundingClientRect(), this._imposterSourceElement);
         return DocumentUtil.offsetDOMRects(
             this._cachedRects,