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Fix scroll sync to work in both directions #122

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Fix scroll sync to work in both directions #122

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39 changes: 36 additions & 3 deletions src/main.js
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Original file line number Diff line number Diff line change
Expand Up @@ -6,6 +6,7 @@ import DOMPurify from 'dompurify';
const init = () => {
let hasEdited = false;
let scrollBarSync = false;
let isScrolling = false;

const localStorageNamespace = 'com.markdownlivepreview';
const localStorageKey = 'last_state';
Expand Down Expand Up @@ -119,9 +120,9 @@ This web site is using ${"`"}markedjs/marked${"`"}.
});

editor.onDidScrollChange((e) => {
if (!scrollBarSync) {
return;
}
if (!scrollBarSync || isScrolling) return;

isScrolling = true;

const scrollTop = e.scrollTop;
const scrollHeight = e.scrollHeight;
Expand All @@ -133,8 +134,40 @@ This web site is using ${"`"}markedjs/marked${"`"}.
let previewElement = document.querySelector('#preview');
let targetY = (previewElement.scrollHeight - previewElement.clientHeight) * scrollRatio;
previewElement.scrollTo(0, targetY);

requestAnimationFrame(() => { isScrolling = false; });
});

let previewElement = document.querySelector('#preview');

previewElement.addEventListener('scroll', () => {
if (!scrollBarSync || isScrolling) return;

isScrolling = true;

const scrollTop = previewElement.scrollTop;
const scrollHeight = previewElement.scrollHeight;
const clientHeight = previewElement.clientHeight;

const maxScrollTop = scrollHeight - clientHeight;
const scrollRatio = scrollTop / maxScrollTop;

const editorScrollHeight = editor.getScrollHeight();
const editorHeight = editor.getLayoutInfo().height;
const editorMaxScroll = editorScrollHeight - editorHeight;

editor.setScrollTop(editorMaxScroll * scrollRatio);

requestAnimationFrame(() => { isScrolling = false; });
});

previewElement.addEventListener('wheel', (e) => {
if (!scrollBarSync) return;

e.preventDefault();
previewElement.scrollTop += e.deltaY;
}, { passive: false });

return editor;
};

Expand Down