From 9ef4bb15c664617d8fa5e25e376b72b7530322a7 Mon Sep 17 00:00:00 2001
From: Henrik Giesel <hengiesel@gmail.com>
Date: Sat, 7 Aug 2021 03:37:03 +0200
Subject: [PATCH] Fix return behavior on Mathjax decorated element

---
 ts/editable/mathjax-component.ts | 15 +++++++++++++++
 1 file changed, 15 insertions(+)

diff --git a/ts/editable/mathjax-component.ts b/ts/editable/mathjax-component.ts
index 2be18fec6..91ec7b33d 100644
--- a/ts/editable/mathjax-component.ts
+++ b/ts/editable/mathjax-component.ts
@@ -40,12 +40,25 @@ function placeCaretAfter(node: Node): void {
 
 function moveNodesInsertedOutside(element: Element, allowedChild: Node): () => void {
     const observer = new MutationObserver(() => {
+        if (element.childNodes.length === 1) {
+            return;
+        }
+
         const childNodes = [...element.childNodes];
         const allowedIndex = childNodes.findIndex((child) => child === allowedChild);
 
         const beforeChildren = childNodes.slice(0, allowedIndex);
         const afterChildren = childNodes.slice(allowedIndex + 1);
 
+        // Special treatment for pressing return after mathjax block
+        if (
+            afterChildren.length === 2 &&
+            afterChildren.every((child) => (child as Element).tagName === "BR")
+        ) {
+            const first = afterChildren.pop();
+            element.removeChild(first!);
+        }
+
         let lastNode: Node | null = null;
 
         for (const node of beforeChildren) {
@@ -140,6 +153,7 @@ export const Mathjax: DecoratedElementConstructor = class Mathjax
     decorate(): void {
         const mathjax = (this.dataset.mathjax = this.innerText);
         this.innerHTML = "";
+        this.style.whiteSpace = "normal";
 
         this.component = new Mathjax_svelte({
             target: this,
@@ -150,6 +164,7 @@ export const Mathjax: DecoratedElementConstructor = class Mathjax
     undecorate(): void {
         this.innerHTML = this.dataset.mathjax ?? "";
         delete this.dataset.mathjax;
+        this.removeAttribute("style");
 
         this.component?.$destroy();
         this.component = undefined;