From 172138f6753a345f5f54168a71f9562115127c7d Mon Sep 17 00:00:00 2001 From: Mudit Ameta Date: Wed, 29 Nov 2023 22:28:23 +0100 Subject: [PATCH] loader: speed up line length calc used by moduleProvider When using a loader, for say TypeScript, the esm loader invokes the `lineLengths` function via `maybeCacheSourceMap` when sourcemaps are enabled. Therefore, `lineLengths` ends up getting called quite often when running large servers written in TypeScript for example. Making `lineLengths` faster should therefore speed up server startup times for anyone using a loader with node with sourcemaps enabled. The change itself is fairly simple and is all about removing creation of unnecessary memory and iterating the whole source content only once with the hope of making the function cache friendly. --- lib/internal/source_map/source_map_cache.js | 24 +++++++++++++++------ 1 file changed, 18 insertions(+), 6 deletions(-) diff --git a/lib/internal/source_map/source_map_cache.js b/lib/internal/source_map/source_map_cache.js index 2813da21dfdc63..31fb3b3e5fe2f1 100644 --- a/lib/internal/source_map/source_map_cache.js +++ b/lib/internal/source_map/source_map_cache.js @@ -205,14 +205,26 @@ function dataFromUrl(sourceURL, sourceMappingURL) { // from. This allows translation from byte offset V8 coverage reports, // to line/column offset Source Map V3. function lineLengths(content) { - // We purposefully keep \r as part of the line-length calculation, in - // cases where there is a \r\n separator, so that this can be taken into - // account in coverage calculations. - return ArrayPrototypeMap(RegExpPrototypeSymbolSplit(/\n|\u2028|\u2029/, content), (line) => { - return line.length; - }); + const contentLength = content.length; + const output = []; + let lineLength = 0 + for (let i = 0; i < contentLength; i++, lineLength++) { + const codePoint = content.codePointAt(i); + + // We purposefully keep \r as part of the line-length calculation, in + // cases where there is a \r\n separator, so that this can be taken into + // account in coverage calculations. + // codepoints for \n, \u2028 and \u2029 + if (codePoint === 10 || codePoint === 0x2028 || codePoint === 0x2029) { + output.push(lineLength); + lineLength = -1; // to not count the matched codePoint such as \n character + } + } + output.push(lineLength); + return output; } + function sourceMapFromFile(mapURL) { try { const fs = require('fs');