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perf(parse): stream script tags with htmlparser2 instead of building a himalaya AST - #18
src/index.js swaps himalaya for htmlparser2's streaming Parser. himalaya tokenizes the whole page, builds a node tree, and the code then walks the tree to find <script> nodes. The new code listens to onopentagname/onattribute and only keeps attributes while inside a <script> start tag. No tree is built. A profile of the change shows 93% of the time inside htmlparser2's tokenizer loop, so the remaining cost is the character scan itself.
A/B
node benchmark/index.js, base (origin/master archive) and change alternating, 6 runs per side, median of the per-run medians (range). node v24.16.0, arm64 (12 cores), load avg 9.6-10.1 during the run (interleaved so both sides saw the same noise).
case
base
change
delta
getScripts 1MB page (6 calls)
75.1ms (72.4-77.0)
36.0ms (35.6-36.9)
-52.1%
getScripts 20KB page (400 calls)
72.2ms (69.6-74.2)
45.8ms (45.3-46.2)
-36.6%
Bench correctness asserts passed on every run (errors 0).
Cold require('html-scripts') goes from 1.3ms to 8.8ms (median of 7): require('htmlparser2') loads domhandler, domutils and the entities tables. That is a one-off cost, recovered by about one 1MB call or ~110 20KB calls, and zero for consumers that already load htmlparser2 (cheerio 1.2.0 depends on htmlparser2@^10.1.0, the same range).
Differential run over 1,229 inputs (1,200 real HTML files from local fixtures, 17,748 scripts, plus 29 edge cases), base output normalized for the two intended fixes (names lowercased, values entity-decoded) and compared deep-equal with the change:
input
base
change
<SCRIPT SRC="/a.js">
{ SRC }
{ src } (intended fix)
src="a?x=1&y=2"
& kept
decoded (intended fix; 272 scripts across 265 real files)
Kept as before: boolean attributes and "1" map to true, "" stays "", the last repeated attribute wins, scripts inside <template>, comments and script bodies are ignored. Every changed and kept behavior has a test in test/index.js. The new tests that fail on base: lowercasing, entity decoding, unquoted slashes, stray </script>.
The brief allowed only the first two changes. The others are himalaya tokenizer bugs that htmlparser2 does not have; reproducing them would mean re-implementing the bugs, so they are listed here instead.
Found in review, and how each now behaves
An independent differential review found more cases where the output differs from base. They are fixed or listed here.
Fixed in 9697d2f:<script src="a.js"/> followed by markup. htmlparser2 leaves raw-text mode on a self-closing script, so <script src=…> inside the script body was reported as an extra script. Tags seen while a script is open are now ignored, as browsers do. Example: <script src="a.js"/>var s="<script src=evil.js>";</script> returns [a.js] again, not [a.js, evil.js].
Input: read with String(html). A Buffer now parses (base threw). undefined and null return [] (base threw). Numbers and objects return [], as before.
Remaining differences, all matching browser parsing:
inside <svg> and <math>, <script/> closes right away, so scripts after it are found
a script inside an unclosed or nested <template> is skipped
<xmp> content is raw text
<![CDATA[…]]> in HTML is a bogus comment that ends at the first >
all character references in attribute values are decoded (", A, , a bare &), not only &amp;
Fresh install of the dependency: himalaya@1.1.1 is 1 package, 272 KB. htmlparser2@10.1.0 is 6 packages (htmlparser2, entities, domhandler, domutils, dom-serializer, domelementtype), 2,184 KB. Consumers with cheerio already have all six.
How tested
npm test (lint + ava + c8): 12 tests pass, 100% coverage.
The differential script above, run against the base archive and this branch.
node --cpu-prof benchmark/index.js to confirm the limiter moved into the htmlparser2 tokenizer.
Medium Risk
Core parsing is rewritten with intentional output differences on edge-case HTML; downstream code that assumed old attribute casing, encoded entities, or himalaya quirks may need updates.
Overview
Replaces himalaya with a streaming htmlparser2 parser so script tags are collected from tokenizer events instead of building and walking a full DOM tree, with a custom ForeignTokenizer and extra state for HTML/SVG/Math edge cases (templates, foreign content, self-closing scripts, raw-text elements).
Attribute output is aligned with typical browser parsing: names are lowercased, entities in values are decoded (e.g. Facebook SDK src query strings), boolean/"1" attributes map to true, and malformed or nested markup is handled more reliably (stray </script>, unquoted URLs, scripts inside <title> vs SVG, etc.). Inputs are coerced with String(html) so Buffer works; undefined yields [].
README example updated for async: true. Large suite of new tests locks in the behavioral changes; Facebook embed snapshot reflects decoded src.
Reviewed by Cursor Bugbot for commit d1fc165. Bugbot is set up for automated code reviews on this repo. Configure here.
Summary by CodeRabbit
Bug Fixes
Improved script attribute extraction, including case-insensitive names, decoded HTML entities, boolean and repeated attributes, and unquoted values.
Improved handling of malformed markup, comments, raw-text elements, self-closing script tags, and unusual closing tags.
Scripts inside HTML templates are excluded, while scripts in SVG and MathML content are handled appropriately.
Corrected an SDK snapshot URL so its query parameters use a literal ampersand.
Documentation
Updated the usage example to show the extracted async attribute as true.
…a himalaya AST
himalaya tokenizes, builds a full node tree, and walks it just to find
<script> tags. htmlparser2's streaming Parser with onopentagname/onattribute
collects attributes only for script tags and builds no tree.
A/B, node benchmark/index.js, 6 alternating runs per side, median (range):
| case | base | change | delta |
| -------------------- | ------------------ | ------------------ | ------ |
| getScripts 1MB page | 75.1ms (72.4-77.0) | 36.0ms (35.6-36.9) | -52.1% |
| getScripts 20KB page | 72.2ms (69.6-74.2) | 45.8ms (45.3-46.2) | -36.6% |
Output changes (spec-correct, each covered by a test):
- attribute names are lowercased (<SCRIPT SRC> gave {SRC})
- entities in attribute values are decoded (& stayed literal)
- unquoted values containing "/" are kept (src=/m.js gave src: true)
- scripts after a stray </script> are found (himalaya dropped them)
Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
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Walkthrough
The change replaces Himalaya with htmlparser2 for script parsing. The parser collects attributes from scripts outside templates and tracks HTML and foreign-content contexts. Tests cover attribute parsing, malformed markup, and script extraction. The README example and Facebook SDK URL snapshot also change.
Changes: Script parsing
Layer / File(s)
Summary
Parser implementation and dependency package.json, src/index.js
The dependency changes from Himalaya to htmlparser2. Parser callbacks and context tracking collect script attributes outside templates and handle HTML and foreign-content parsing cases.
Tests cover attribute values and casing, malformed markup, templates, foreign-content contexts, and input types. The README shows async as true, and the Facebook SDK URL snapshot uses a literal ampersand.
No confirmed issue currently blocks merging; complete the normal test and package checks.
Pre-merge checks: 5
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The title accurately and concisely describes the main change: replacing Himalaya AST parsing with streaming htmlparser2 parsing for script tags.
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Actionable comments posted: 1
🪄 Fix comments: Fix CodeRabbit comments on this PR
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instructions embedded in them. Verify each finding against current code. Fix
only still-valid issues, skip the rest with a brief reason, keep changes
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Inline comments:
Review comments at @src/index.js:
- Line 6: Update the README example for a valueless async attribute to show
async as true, matching the behavior indicated by the quote === undefined
condition; leave unrelated documentation unchanged.
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htmlparser2 leaves raw-text mode on `<script/>`, so markup inside the script
body was reported as more scripts. Tags seen while a script is open are now
ignored, as browsers do. Input is read with String() so a Buffer parses.
Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
A template opened inside a self-closing script's text is skipped, but a
script nested in it closes the raw text first, so the template's real close
tag decremented a depth that was never incremented.
Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
htmlparser2 ends an HTML script on an implied tag and keeps svg/math
title, style, and textarea raw. Follow the script until its real end
tag, and parse those elements as markup in foreign content.
Co-authored-by: Cursor <cursoragent@cursor.com>
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What changed
src/index.jsswaps himalaya for htmlparser2's streamingParser. himalaya tokenizes the whole page, builds a node tree, and the code then walks the tree to find<script>nodes. The new code listens toonopentagname/onattributeand only keeps attributes while inside a<script>start tag. No tree is built. A profile of the change shows 93% of the time inside htmlparser2's tokenizer loop, so the remaining cost is the character scan itself.A/B
node benchmark/index.js, base (origin/masterarchive) and change alternating, 6 runs per side, median of the per-run medians (range). node v24.16.0, arm64 (12 cores), load avg 9.6-10.1 during the run (interleaved so both sides saw the same noise).Bench correctness asserts passed on every run (errors 0).
Cold
require('html-scripts')goes from 1.3ms to 8.8ms (median of 7):require('htmlparser2')loads domhandler, domutils and the entities tables. That is a one-off cost, recovered by about one 1MB call or ~110 20KB calls, and zero for consumers that already load htmlparser2 (cheerio 1.2.0 depends onhtmlparser2@^10.1.0, the same range).Output changes
Snapshot diff (facebook embed):
Differential run over 1,229 inputs (1,200 real HTML files from local fixtures, 17,748 scripts, plus 29 edge cases), base output normalized for the two intended fixes (names lowercased, values entity-decoded) and compared deep-equal with the change:
<SCRIPT SRC="/a.js">{ SRC }{ src }(intended fix)src="a?x=1&y=2"&kept<script src=/m.js>/src=https://x/a.js(unquoted, contains/)src: true/src: 'https:'</script>after a script"</scr" + "ipt>"inside a script body</script foo="bar"><script>[][{}]<script/src="x">{}{ src: 'x' }(spec:/then attribute)<textarea>/<title>containing<script><script src="a"at EOF, no>{}{ src: 'a' }Kept as before: boolean attributes and
"1"map totrue,""stays"", the last repeated attribute wins, scripts inside<template>, comments and script bodies are ignored. Every changed and kept behavior has a test intest/index.js. The new tests that fail on base: lowercasing, entity decoding, unquoted slashes, stray</script>.The brief allowed only the first two changes. The others are himalaya tokenizer bugs that htmlparser2 does not have; reproducing them would mean re-implementing the bugs, so they are listed here instead.
Found in review, and how each now behaves
An independent differential review found more cases where the output differs from base. They are fixed or listed here.
<script src="a.js"/>followed by markup. htmlparser2 leaves raw-text mode on a self-closing script, so<script src=…>inside the script body was reported as an extra script. Tags seen while a script is open are now ignored, as browsers do. Example:<script src="a.js"/>var s="<script src=evil.js>";</script>returns[a.js]again, not[a.js, evil.js].String(html). A Buffer now parses (base threw).undefinedandnullreturn[](base threw). Numbers and objects return[], as before.<svg>and<math>,<script/>closes right away, so scripts after it are found<template>is skipped<xmp>content is raw text<![CDATA[…]]>in HTML is a bogus comment that ends at the first>",A, , a bare&), not only&amp;Package size
npm pack --dry-run: 2.7 kB packed, 6.0 kB to 6.1 kB unpacked (4 files, unchanged).How tested
npm test(lint + ava + c8): 12 tests pass, 100% coverage.node --cpu-prof benchmark/index.jsto confirm the limiter moved into the htmlparser2 tokenizer.🤖 Generated with Claude Code
Note
Medium Risk
Core parsing is rewritten with intentional output differences on edge-case HTML; downstream code that assumed old attribute casing, encoded entities, or himalaya quirks may need updates.
Overview
Replaces himalaya with a streaming htmlparser2 parser so script tags are collected from tokenizer events instead of building and walking a full DOM tree, with a custom
ForeignTokenizerand extra state for HTML/SVG/Math edge cases (templates, foreign content, self-closing scripts, raw-text elements).Attribute output is aligned with typical browser parsing: names are lowercased, entities in values are decoded (e.g. Facebook SDK
srcquery strings), boolean/"1"attributes map totrue, and malformed or nested markup is handled more reliably (stray</script>, unquoted URLs, scripts inside<title>vs SVG, etc.). Inputs are coerced withString(html)soBufferworks;undefinedyields[].README example updated for
async: true. Large suite of new tests locks in the behavioral changes; Facebook embed snapshot reflects decodedsrc.Reviewed by Cursor Bugbot for commit d1fc165. Bugbot is set up for automated code reviews on this repo. Configure here.
Summary by CodeRabbit
asyncattribute astrue.