Minor refactoring in LexicalLineBreakNode (#5455)

packages/lexical/src/nodes/LexicalLineBreakNode.ts

@@ -50,25 +50,7 @@ export class LineBreakNode extends LexicalNode {
   static importDOM(): DOMConversionMap | null {
     return {
       br: (node: Node) => {
-        const parentElement = node.parentElement;
-        // If the <br> is the only child, then skip including it
-        let firstChild;
-        let lastChild;
-        if (
-          parentElement !== null &&
-          ((firstChild = parentElement.firstChild) === node ||
-            ((firstChild as Text).nextSibling === node &&
-              (firstChild as Text).nodeType === DOM_TEXT_TYPE &&
-              ((firstChild as Text).textContent || '').match(
-                /^( |\t|\r?\n)+$/,
-              ) !== null)) &&
-          ((lastChild = parentElement.lastChild) === node ||
-            ((lastChild as Text).previousSibling === node &&
-              (lastChild as Text).nodeType === DOM_TEXT_TYPE &&
-              ((lastChild as Text).textContent || '').match(
-                /^( |\t|\r?\n)+$/,
-              ) !== null))
-        ) {
+        if (isOnlyChild(node)) {
           return null;
         }
         return {
@@ -106,3 +88,31 @@ export function $isLineBreakNode(
 ): node is LineBreakNode {
   return node instanceof LineBreakNode;
 }
+
+function isOnlyChild(node: Node): boolean {
+  const parentElement = node.parentElement;
+  if (parentElement !== null) {
+    const firstChild = parentElement.firstChild!;
+    if (
+      firstChild === node ||
+      (firstChild.nextSibling === node && isWhitespaceDomTextNode(firstChild))
+    ) {
+      const lastChild = parentElement.lastChild!;
+      if (
+        lastChild === node ||
+        (lastChild.previousSibling === node &&
+          isWhitespaceDomTextNode(lastChild))
+      ) {
+        return true;
+      }
+    }
+  }
+  return false;
+}
+
+function isWhitespaceDomTextNode(node: Node): boolean {
+  return (
+    node.nodeType === DOM_TEXT_TYPE &&
+    /^( |\t|\r?\n)+$/.test(node.textContent || '')
+  );
+}