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Merged
domenic merged 6 commits into from
Dec 31, 2025
Merged

Add LRU cache for CSS parsing and validation #271

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0a6e828
Add LRU cache utility module
asamuzaK Dec 27, 2025
bb02056
Add caching to property value parsing functions
asamuzaK Dec 27, 2025
8622e7a
Sort exports
asamuzaK Dec 27, 2025
a4bf2a1
Remove null sentinel
asamuzaK Dec 31, 2025
88f76d8
Add lru-cache in parsers.js
asamuzaK Dec 31, 2025
1b2c0b8
Update parsers.js
asamuzaK Dec 31, 2025
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209 changes: 125 additions & 84 deletions lib/parsers.js
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Original file line number Diff line number Diff line change
Expand Up @@ -6,6 +6,7 @@ const {
} = require("@asamuzakjp/css-color");
const { next: syntaxes } = require("@csstools/css-syntax-patches-for-csstree");
const csstree = require("css-tree");
const { LRUCache } = require("lru-cache");
const { asciiLowercase } = require("./utils/strings");

// CSS global keywords
Expand Down Expand Up @@ -86,6 +87,11 @@ const varContainedRegEx = /(?<=[*/\s(])var\(/;
// Patched css-tree
const cssTree = csstree.fork(syntaxes);

// Instance of the LRU Cache. Stores up to 4096 items.
const lruCache = new LRUCache({
max: 4096
});

/**
* Prepares a stringified value.
*
Expand Down Expand Up @@ -192,16 +198,23 @@ const isValidPropertyValue = (prop, val) => {
}
return false;
}
let ast;
const cacheKey = `isValidPropertyValue_${prop}_${val}`;
const cachedValue = lruCache.get(cacheKey);
if (typeof cachedValue === "boolean") {
return cachedValue;
}
let result;
try {
ast = parseCSS(val, {
const ast = parseCSS(val, {
context: "value"
});
const { error, matched } = cssTree.lexer.matchProperty(prop, ast);
result = error === null && matched !== null;
} catch {
return false;
result = false;
}
const { error, matched } = cssTree.lexer.matchProperty(prop, ast);
return error === null && matched !== null;
lruCache.set(cacheKey, result);
return result;
};

/**
Expand All @@ -218,6 +231,11 @@ const resolveCalc = (val, opt = { format: "specifiedValue" }) => {
if (val === "" || hasVarFunc(val) || !hasCalcFunc(val)) {
return val;
}
const cacheKey = `resolveCalc_${val}`;
const cachedValue = lruCache.get(cacheKey);
if (typeof cachedValue === "string") {
return cachedValue;
}
const obj = parseCSS(val, { context: "value" }, true);
if (!obj?.children) {
return;
Expand All @@ -243,7 +261,9 @@ const resolveCalc = (val, opt = { format: "specifiedValue" }) => {
values.push(itemName ?? itemValue);
}
}
return values.join(" ");
const resolvedValue = values.join(" ");
lruCache.set(cacheKey, resolvedValue);
return resolvedValue;
};

/**
Expand All @@ -269,123 +289,144 @@ const parsePropertyValue = (prop, val, opt = {}) => {
}
val = calculatedValue;
}
const cacheKey = `parsePropertyValue_${prop}_${val}_${caseSensitive}`;
const cachedValue = lruCache.get(cacheKey);
if (cachedValue === false) {
return;
} else if (inArray) {
if (Array.isArray(cachedValue)) {
return cachedValue;
}
} else if (typeof cachedValue === "string") {
return cachedValue;
}
let parsedValue;
const lowerCasedValue = asciiLowercase(val);
if (GLOBAL_KEYS.has(lowerCasedValue)) {
if (inArray) {
return [
parsedValue = [
{
type: AST_TYPES.GLOBAL_KEYWORD,
name: lowerCasedValue
}
];
} else {
parsedValue = lowerCasedValue;
}
return lowerCasedValue;
} else if (SYS_COLORS.has(lowerCasedValue)) {
if (/^(?:(?:-webkit-)?(?:[a-z][a-z\d]*-)*color|border)$/i.test(prop)) {
if (inArray) {
return [
parsedValue = [
{
type: AST_TYPES.IDENTIFIER,
name: lowerCasedValue
}
];
} else {
parsedValue = lowerCasedValue;
}
return lowerCasedValue;
}
return;
}
try {
const ast = parseCSS(val, {
context: "value"
});
const { error, matched } = cssTree.lexer.matchProperty(prop, ast);
if (error || !matched) {
return;
} else {
parsedValue = false;
}
if (inArray) {
const obj = cssTree.toPlainObject(ast);
const items = obj.children;
const parsedValues = [];
for (const item of items) {
const { children, name, type, value, unit } = item;
switch (type) {
case AST_TYPES.DIMENSION: {
parsedValues.push({
type,
value,
unit: asciiLowercase(unit)
});
break;
}
case AST_TYPES.FUNCTION: {
const css = cssTree
.generate(item)
.replace(/\)(?!\)|\s|,)/g, ") ")
.trim();
const raw = items.length === 1 ? val : css;
// Remove "${name}(" from the start and ")" from the end
const itemValue = raw.slice(name.length + 1, -1).trim();
if (name === "calc") {
if (children.length === 1) {
const [child] = children;
if (child.type === AST_TYPES.NUMBER) {
parsedValues.push({
type: AST_TYPES.CALC,
isNumber: true,
value: `${parseFloat(child.value)}`,
name,
raw
});
} else {
try {
const ast = parseCSS(val, {
context: "value"
});
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@domenic domenic Dec 31, 2025

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Sorry, I just noticed. Why does this use { context: "value" } but the other one use { options: { context: "value" } }? Is there a hidden bug here?

(I was wondering if we might get some performance by caching parseCSS() results, i.e., sharing the cache between parsePropertyValue and isValidPropertyValue. But, that could be a followup anyway, so it is not blocking.)

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@asamuzaK asamuzaK Dec 31, 2025

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1b2c0b8

Thanks for the catch, was a typo...
{ context: "value" } is the correct option for csstree.

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@domenic domenic Dec 31, 2025

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I worry a bit that our test coverage didn't catch this, but oh well...

const { error, matched } = cssTree.lexer.matchProperty(prop, ast);
if (error || !matched) {
parsedValue = false;
} else if (inArray) {
const obj = cssTree.toPlainObject(ast);
const items = obj.children;
const values = [];
for (const item of items) {
const { children, name, type, value, unit } = item;
switch (type) {
case AST_TYPES.DIMENSION: {
values.push({
type,
value,
unit: asciiLowercase(unit)
});
break;
}
case AST_TYPES.FUNCTION: {
const css = cssTree
.generate(item)
.replace(/\)(?!\)|\s|,)/g, ") ")
.trim();
const raw = items.length === 1 ? val : css;
// Remove "${name}(" from the start and ")" from the end
const itemValue = raw.slice(name.length + 1, -1).trim();
if (name === "calc") {
if (children.length === 1) {
const [child] = children;
if (child.type === AST_TYPES.NUMBER) {
values.push({
type: AST_TYPES.CALC,
isNumber: true,
value: `${parseFloat(child.value)}`,
name,
raw
});
} else {
values.push({
type: AST_TYPES.CALC,
isNumber: false,
value: `${asciiLowercase(itemValue)}`,
name,
raw
});
}
} else {
parsedValues.push({
values.push({
type: AST_TYPES.CALC,
isNumber: false,
value: `${asciiLowercase(itemValue)}`,
value: asciiLowercase(itemValue),
name,
raw
});
}
} else {
parsedValues.push({
type: AST_TYPES.CALC,
isNumber: false,
value: asciiLowercase(itemValue),
values.push({
type,
name,
value: asciiLowercase(itemValue),
raw
});
}
} else {
parsedValues.push({
type,
name,
value: asciiLowercase(itemValue),
raw
});
break;
}
break;
}
case AST_TYPES.IDENTIFIER: {
if (caseSensitive) {
parsedValues.push(item);
} else {
parsedValues.push({
type,
name: asciiLowercase(name)
});
case AST_TYPES.IDENTIFIER: {
if (caseSensitive) {
values.push(item);
} else {
values.push({
type,
name: asciiLowercase(name)
});
}
break;
}
default: {
values.push(item);
}
break;
}
default: {
parsedValues.push(item);
}
}
parsedValue = values;
} else {
parsedValue = val;
}
return parsedValues;
} catch {
parsedValue = false;
}
} catch {
}
lruCache.set(cacheKey, parsedValue);
if (parsedValue === false) {
return;
}
return val;
return parsedValue;
};

/**
Expand Down
3 changes: 2 additions & 1 deletion package-lock.json
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3 changes: 2 additions & 1 deletion package.json
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Original file line number Diff line number Diff line change
Expand Up @@ -18,7 +18,8 @@
"dependencies": {
"@asamuzakjp/css-color": "^4.1.1",
"@csstools/css-syntax-patches-for-csstree": "^1.0.21",
"css-tree": "^3.1.0"
"css-tree": "^3.1.0",
"lru-cache": "^11.2.4"
},
"devDependencies": {
"@babel/generator": "^7.28.5",
Expand Down