util: create hex style cache and fast path

benchmark/util/style-text.js

@@ -5,9 +5,22 @@ const common = require('../common.js');
 const { styleText } = require('node:util');
 const assert = require('node:assert');
 
+// 1000 distinct hex colors to exercise the cache under high-miss conditions.
+// Spread evenly across hue space so colors are valid and maximally varied.
+const kHexColorCount = 1000;
+const toHex = (n) => n.toString(16).padStart(2, '0');
+const hexColors = Array.from({ length: kHexColorCount }, (_, i) => {
+  const r = (i * 37) & 0xff;
+  const g = (i * 73) & 0xff;
+  const b = (i * 137) & 0xff;
+  return `#${toHex(r)}${toHex(g)}${toHex(b)}`;
+});
+
 const bench = common.createBenchmark(main, {
   messageType: ['string', 'number', 'boolean', 'invalid'],
-  format: ['red', 'italic', 'invalid', '#ff0000'],
+  // '#rotating' cycles through kHexColorCount distinct colors to simulate
+  // the high-miss-rate / large-cache scenario (e.g. user-randomised colors).
+  format: ['red', 'italic', 'invalid', '#ff0000', '#rotating'],
   validateStream: [1, 0],
   n: [1e3],
 });
@@ -31,9 +44,10 @@ function main({ messageType, format, validateStream, n }) {
 
   bench.start();
   for (let i = 0; i < n; i++) {
+    const fmt = format === '#rotating' ? hexColors[i % kHexColorCount] : format;
     let colored = '';
     try {
-      colored = styleText(format, str, { validateStream });
+      colored = styleText(fmt, str, { validateStream });
       assert.ok(colored); // Attempt to avoid dead-code elimination
     } catch {
       // eslint-disable no-empty

lib/util.js

@@ -38,6 +38,7 @@ const {
   ObjectValues,
   ReflectApply,
   RegExpPrototypeExec,
+  SafeMap,
   StringPrototypeSlice,
   StringPrototypeToWellFormed,
 } = primordials;
@@ -114,8 +115,34 @@ const kEscapeEnd = 'm';
 const kDimCode = 2;
 const kBoldCode = 1;
 
+// Close sequence for 24-bit foreground colors (reset to default foreground)
+const kHexCloseSeq = kEscape + '39' + kEscapeEnd;
+
 let styleCache;
 
+const kHexStyleCacheMax = 256;
+
+class HexStyleFIFOCache {
+  #cache = new SafeMap();
+
+  get(key) {
+    return this.#cache.get(key);
+  }
+
+  set(key, value) {
+    if (this.#cache.size >= kHexStyleCacheMax)
+      this.#cache.delete(this.#cache.keys().next().value);
+    this.#cache.set(key, value);
+  }
+}
+
+let hexStyleCache;
+
+function getHexStyleCache() {
+  hexStyleCache ??= new HexStyleFIFOCache();
+  return hexStyleCache;
+}
+
 function getStyleCache() {
   if (styleCache === undefined) {
     styleCache = { __proto__: null };
@@ -137,6 +164,26 @@ function getStyleCache() {
   return styleCache;
 }
 
+/**
+ * Returns the cached ANSI escape sequences for a hex color.
+ * Computes and caches on first use to avoid repeated Buffer allocations.
+ * @param {string} hex A valid hex color string (#RGB or #RRGGBB)
+ * @returns {{openSeq: string, closeSeq: string}}
+ */
+function getHexStyle(hex) {
+  const cache = getHexStyleCache();
+  const cached = cache.get(hex);
+  if (cached !== undefined) return cached;
+  const { 0: r, 1: g, 2: b } = hexToRgb(hex);
+  const style = {
+    __proto__: null,
+    openSeq: kEscape + rgbToAnsi24Bit(r, g, b) + kEscapeEnd,
+    closeSeq: kHexCloseSeq,
+  };
+  cache.set(hex, style);
+  return style;
+}
+
 function replaceCloseCode(str, closeSeq, openSeq, keepClose) {
   const closeLen = closeSeq.length;
   let index = str.indexOf(closeSeq);
@@ -163,15 +210,6 @@ function replaceCloseCode(str, closeSeq, openSeq, keepClose) {
 // Matches #RGB or #RRGGBB
 const hexColorRegExp = /^#(?:[0-9a-fA-F]{3}|[0-9a-fA-F]{6})$/;
 
-/**
- * Validates whether a string is a valid hex color code.
- * @param {string} hex The hex string to validate (e.g., '#fff' or '#ffffff')
- * @returns {boolean} True if valid hex color, false otherwise
- */
-function isValidHexColor(hex) {
-  return typeof hex === 'string' && RegExpPrototypeExec(hexColorRegExp, hex) !== null;
-}
-
 /**
  * Parses a hex color string into RGB components.
  * Supports both 3-digit (#RGB) and 6-digit (#RRGGBB) formats.
@@ -225,6 +263,17 @@ function styleText(format, text, options) {
       const processed = replaceCloseCode(text, style.closeSeq, style.openSeq, style.keepClose);
       return style.openSeq + processed + style.closeSeq;
     }
+
+    if (format[0] === '#') {
+      let hexStyle = getHexStyleCache().get(format);
+      if (hexStyle === undefined && RegExpPrototypeExec(hexColorRegExp, format) !== null) {
+        hexStyle = getHexStyle(format);
+      }
+      if (hexStyle !== undefined) {
+        const processed = replaceCloseCode(text, hexStyle.closeSeq, hexStyle.openSeq, false);
+        return hexStyle.openSeq + processed + hexStyle.closeSeq;
+      }
+    }
   }
 
   validateString(text, 'text');
@@ -255,24 +304,26 @@ function styleText(format, text, options) {
   for (const key of formatArray) {
     if (key === 'none') continue;
 
-    if (isValidHexColor(key)) {
-      if (skipColorize) continue;
-      const { 0: r, 1: g, 2: b } = hexToRgb(key);
-      const openSeq = kEscape + rgbToAnsi24Bit(r, g, b) + kEscapeEnd;
-      const closeSeq = kEscape + '39' + kEscapeEnd;
-      openCodes += openSeq;
-      closeCodes = closeSeq + closeCodes;
-      processedText = replaceCloseCode(processedText, closeSeq, openSeq, false);
+    if (typeof key === 'string' && key[0] === '#') {
+      let hexStyle = getHexStyleCache().get(key);
+      if (hexStyle === undefined) {
+        if (RegExpPrototypeExec(hexColorRegExp, key) === null) {
+          throw new ERR_INVALID_ARG_VALUE('format', key,
+                                          'must be a valid hex color (#RGB or #RRGGBB)');
+        }
+        if (skipColorize) continue;
+        hexStyle = getHexStyle(key);
+      } else if (skipColorize) {
+        continue;
+      }
+      openCodes += hexStyle.openSeq;
+      closeCodes = hexStyle.closeSeq + closeCodes;
+      processedText = replaceCloseCode(processedText, hexStyle.closeSeq, hexStyle.openSeq, false);
       continue;
     }
 
     const style = cache[key];
     if (style === undefined) {
-      // Check if it looks like an invalid hex color (starts with #)
-      if (typeof key === 'string' && key[0] === '#') {
-        throw new ERR_INVALID_ARG_VALUE('format', key,
-                                        'must be a valid hex color (#RGB or #RRGGBB)');
-      }
       validateOneOf(key, 'format', ObjectGetOwnPropertyNames(inspect.colors));
     }
     openCodes += style.openSeq;