Split type guard into two helper functions

src/annotator/frame-observer.ts

@@ -161,6 +161,10 @@ export function onDocumentReady(
   { pollInterval = 10 }: { pollInterval?: number } = {}
 ): () => void {
   let pollTimer: number | undefined;
+  // Two linting rules are conflicting here, so muting one of them.
+  // This should be fixable by refactoring the whole function, as there are
+  // crossed dependencies between local callbacks, that rely on each other
+  // having been called in a specific order.
   // eslint-disable-next-line prefer-const
   let pollForDocumentChange: () => void;
 

src/annotator/range-util.ts

@@ -52,10 +52,12 @@ export function forEachNodeInRange(range: Range, callback: (n: Node) => void) {
 }
 
 function nodeIsText(node: Node): node is Text {
+  return node.nodeType === Node.TEXT_NODE;
+}
+
+function textNodeContainsText(textNode: Text): boolean {
   const whitespaceOnly = /^\s*$/;
-  return (
-    node.nodeType === Node.TEXT_NODE && !node.textContent!.match(whitespaceOnly)
-  );
+  return !textNode.textContent!.match(whitespaceOnly);
 }
 
 /**
@@ -66,7 +68,7 @@ function nodeIsText(node: Node): node is Text {
 export function getTextBoundingBoxes(range: Range): DOMRect[] {
   const textNodes: Text[] = [];
   forEachNodeInRange(range, node => {
-    if (nodeIsText(node)) {
+    if (nodeIsText(node) && textNodeContainsText(node)) {
       textNodes.push(node);
     }
   });