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Add LaTeX math support to Markdown live preview - #496
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jsgrrchg
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September 28, 2026 19:07
Node rules skipped every syntax node whose start fell inside a formula, so a paragraph, list item or whole note beginning with $x$ lost all its Markdown styling. Only skip nodes that cut through a formula, and look formulas up in the viewport with a binary search.
Every formula was registered as a block range, so highlights, footnote references and inline HTML that merely contained one stopped rendering. Only skip tokens that start or end inside a formula.
Note names may contain dollars, e.g. [[Cost $5 and $x$]]. Treat wikilinks and embeds like link destinations so they keep resolving as links instead of rendering part of the target as a formula.
An inline-block scroll container aligns its bottom edge with the baseline, which raised every inline formula and error above the surrounding text. Use an inline flex container instead, and pad the KaTeX box so the -2px margin of scripts and roots no longer overflows and shows a scrollbar under short formulas on platforms with classic scrollbars.
Math widgets handled every mousedown, so pressing a wide formula's horizontal scrollbar revealed its source instead of scrolling. Let presses below the client area of an overflowing formula reach the native scrollbar.
The math range field reparses on every keystroke. Return early for notes without dollars, walk the syntax tree only across the span that holds them, and jump between dollars instead of visiting every character. In a 700 KB note this cuts reparsing from ~12 ms to ~1 ms without formulas and from ~18 ms to ~14 ms when every line has one. A differential fuzz run over 60,000 generated documents matched the previous parser exactly.
Describe where multiline display math stays literal, the wikilink exclusion, scrollbar behavior and how formulas interact with surrounding Markdown.
Type the elements measured by the new math browser tests so the e2e harness type check passes in CI. Wait for background parsing to finish before jumping to the end of the long-note test: display blocks that appeared after the jump grew the note under the scroll target and failed about one run in four.
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Markdown live preview now renders inline
$…$and display$$…$$formulas using the existing KaTeX dependency. Click a formula or move the caret into it to edit its LaTeX source; leaving the formula restores its preview.The shared delimiter parser keeps common dollar prices, escaped dollars, code, frontmatter, and link destinations literal. Single-line and multiline display formulas use display layout, wide formulas scroll horizontally, and invalid formulas remain readable and editable. The Markdown source is preserved through edits, undo/redo, tab switches, and source/preview mode changes.
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Validation
main.docs/markdown-math.md.Pre-merge audit fixes
An audit before merging found regressions against
main, now fixed in separate commits:3568c530): a paragraph, list item, quote or whole note starting with a formula lost all node-based styling (bold, headings, links). Only nodes that cut through a formula are skipped now.291d1081): highlights,<kbd>, footnote references and inline HTML vanished when they contained a whole formula.78612a30):[[Note $x$]]rendered part of the note name as math; wikilinks and embeds are now excluded from math parsing.65b5cbe1): inline formulas and errors sat 9–24 px above the text baseline (inline-block scroll container). Switched to an inline flex container and absorbed KaTeX's-2pxscript margin, which also removes stray 15 px scrollbars under short formulas such asy_1on platforms with classic scrollbars.06ea7041): pressing a wide formula's scrollbar revealed its source instead of scrolling it.af38b4f0): the math range field reparses per keystroke; it now exits early without dollars, walks the syntax tree only across the dollar span and jumps between dollars. In a 700 KB note: ~12 → ~1 ms without formulas, ~15 → ~10 ms with prices, ~18 → ~14 ms with a formula per line. A 60,000-document differential fuzz matched the previous parser exactly.969abb17): documented where multiline display math stays literal (quotes/callouts, after list markers, 4+ space indentation), the wikilink exclusion and scrollbar behavior.Each fix ships with regression tests that fail without it: unit tests for styling, tokens, wikilinks and scrollbar handling, plus browser tests for baseline alignment, stray scrollbars (with real scrollbars enabled) and scrollbar presses.
After the fixes: 594 editor unit tests, the 25-test math/list/tab-rendering browser suite,
tsc, ESLint and the production build pass.Known leftovers: a formula filling a token exactly (
==$x$==) renders without the token's style (CodeMirror mark/widget behavior), and math-dense notes still reparse in O(n).Scope
Supports KaTeX-compatible mathematics, not full LaTeX documents or arbitrary packages. Math inside tables and the alternative
\(…\)/\[…\]delimiters remain outside this initial implementation.