Improve getPreferredQuote (#18366)

benchmarks/get-preferred-quote.js

@@ -0,0 +1,30 @@
+import assert from "node:assert/strict";
+// import * as prettierDevBundled from "../dist/prettier/index.mjs";
+import * as prettierProduction from "../node_modules/prettier/index.mjs";
+import * as prettierDevelopment from "../src/index.js";
+import { runBenchmark } from "./utilities.js";
+
+assert.notEqual(prettierProduction.version, prettierDevelopment.version);
+
+for (const size of [1, 1e1, 1e2, 1e3, 1e4, 1e5]) {
+  const text = Array.from({ length: size }, () =>
+    Math.random() > 0.5 ? " " : Math.random() > 0.5 ? "'" : '"',
+  ).join("");
+  const run = (prettier) => prettier.util.getPreferredQuote(text, "'");
+  const expected = run(prettierProduction);
+
+  await runBenchmark(
+    {
+      name: `getPreferredQuote (${size} characters)`,
+      assert: (result) => assert.deepEqual(result, expected),
+    },
+    [
+      { name: "Development", prettier: prettierDevelopment },
+      // { name: "Development(Bundled)", prettier: prettierDevBundled },
+      { name: "Production", prettier: prettierProduction },
+    ].map(({ name, prettier }) => ({
+      name,
+      implementation: () => run(prettier),
+    })),
+  );
+}

src/utilities/get-preferred-quote.js

@@ -5,31 +5,51 @@
 const SINGLE_QUOTE = "'";
 const DOUBLE_QUOTE = '"';
 
+const SINGLE_QUOTE_DATA = Object.freeze({
+  character: SINGLE_QUOTE,
+  codePoint: 39,
+});
+const DOUBLE_QUOTE_DATA = Object.freeze({
+  character: DOUBLE_QUOTE,
+  codePoint: 34,
+});
+
+const SINGLE_QUOTE_SETTINGS = Object.freeze({
+  preferred: SINGLE_QUOTE_DATA,
+  alternate: DOUBLE_QUOTE_DATA,
+});
+const DOUBLE_QUOTE_SETTINGS = Object.freeze({
+  preferred: DOUBLE_QUOTE_DATA,
+  alternate: SINGLE_QUOTE_DATA,
+});
+
 /**
- *
  * @param {string} text
  * @param {Quote | boolean} preferredQuoteOrPreferSingleQuote
  * @returns {Quote}
  */
 function getPreferredQuote(text, preferredQuoteOrPreferSingleQuote) {
-  const preferred =
+  const { preferred, alternate } =
     preferredQuoteOrPreferSingleQuote === true ||
     preferredQuoteOrPreferSingleQuote === SINGLE_QUOTE
-      ? SINGLE_QUOTE
-      : DOUBLE_QUOTE;
-  const alternate = preferred === SINGLE_QUOTE ? DOUBLE_QUOTE : SINGLE_QUOTE;
-
+      ? SINGLE_QUOTE_SETTINGS
+      : DOUBLE_QUOTE_SETTINGS;
+  const { length } = text;
   let preferredQuoteCount = 0;
   let alternateQuoteCount = 0;
-  for (const character of text) {
-    if (character === preferred) {
+
+  // `for..of` loop is known slower
+  for (let index = 0; index < length; index++) {
+    const codePoint = text.charCodeAt(index);
+    if (codePoint === preferred.codePoint) {
       preferredQuoteCount++;
-    } else if (character === alternate) {
+    } else if (codePoint === alternate.codePoint) {
       alternateQuoteCount++;
     }
   }
 
-  return preferredQuoteCount > alternateQuoteCount ? alternate : preferred;
+  return (preferredQuoteCount > alternateQuoteCount ? alternate : preferred)
+    .character;
 }
 
 export default getPreferredQuote;