0.3.0 • Public • Published


Caches resolved paths in module require to avoid Node hunting for right module. Speeds up app load.


Build status semantic-release

This is a partial solution to Node "hunting" for right file to load when you require a 3rd party dependency. See Node’s require is dog slow and Faster Node app require for details.


npm install --save cache-require-paths

Load the module first in your application file

// index.js

The first time the app loads, a cache of resolved file paths will be saved to .cache-require-paths.json in the current directory. Every application startup after that will reuse this filename cache to avoid "hunting" for the right filename.

To save cached paths to a different file, set the environmental variable CACHE_REQUIRE_PATHS_FILE.


Here are results for loading common packages without and with caching resolved require paths. You can run any of this experiments inside the test folder. node index.js loads using the standard resolve. node index.js --cache uses a cache of the resolves paths.

Using node 0.10.37

require('X')    |  standard (ms)  |  with cache (ms)  |  speedup (%)
express@4.12.3  |        72       |       46          |     36
karma@0.12.31   |       230       |      170          |     26
grunt@0.4.5     |       120       |       95          |     20
sails@0.11.0    |       170       |      120          |     29

Using node 0.12.2 - all startup times became slower.

require('X')    |  standard (ms)  |  with cache (ms)  |  speedup (%)
express@4.12.3  |        90       |       55          |     38
karma@0.12.31   |       250       |      200          |     20
grunt@0.4.5     |       150       |      120          |     20
sails@0.11.0    |       200       |      145          |     27


  • Cache only the absolute paths (relative paths resolve quickly)
  • Invalidate cache if dependencies in the package.json change


You can see Node on Mac OS X searchig for a file to load when loading an absolute path like require(express) by using the following command to make a log of all system level calls from Node (start this from another terminal before running node program)

sudo dtruss -d -n 'node' > /tmp/require.log 2>&1

Then run the test program, for example in the test folder run

$ node index.js

Kill the dtruss process and open the generated /tmp/require.log. It shows every system call with the following 4 columns: process id (should be single node process), relative time (microseconds), system call with arguments, and after the equality sign the numerical result of the call.

When loading express dependency from the test program using require('express'); we see the following search (I abbreviated paths for clarity):

# microseconds call
664730 stat64(".../test/node_modules/express\0", 0x7FFF5FBFECF8, 0x204)        = 0 0
664784 stat64(".../test/node_modules/express.js\0", 0x7FFF5FBFED28, 0x204)         = -1 Err#2
664834 stat64(".../test/node_modules/express.json\0", 0x7FFF5FBFED28, 0x204)       = -1 Err#2
664859 stat64(".../test/node_modules/express.node\0", 0x7FFF5FBFED28, 0x204)       = -1 Err#2
664969 open(".../test/node_modules/express/package.json\0", 0x0, 0x1B6)        = 11 0
664976 fstat64(0xB, 0x7FFF5FBFEC38, 0x1B6)         = 0 0
665022 read(0xB, "{\n  \"name\": \"express\", ...}", 0x103D)        = 4157 0
665030 close(0xB)      = 0 0

By default, Node checks if the local node_modules/express folder exists first (first stat64 call), Then it tries to check the status of the node_modules/express.js file and fails. Then node_modules/express.json file. Then node_modules/express.node file. Finally it opens the node_modules/express/package.json file and reads the contents.

Note that this is not the end of the story. Node loader only loads express/package.json to fetch main filename or use the default index.js! Each wasted file system call takes only 100 microseconds, but the tiny delays add up to hundreds of milliseconds and finally seconds for larger frameworks.

Profile the same program with --cache option added to the command line arguments

$ node index.js --cache

This option loads the cache-require-paths module as the first require of the application

var useCache = process.argv.some(function (str) {
  return str === '--cache';
if (useCache) {
  console.log('using filename cache');

The trace now shows no calls to find express package, just straight load of the express/index.js file.

643466 stat64(".../node_modules/express/index.js\0", 0x7FFF5FBFED28, 0x3)         = 0 0
643501 lstat64(".../node_modules\0", 0x7FFF5FBFED08, 0x3)         = 0 0
643513 lstat64(".../node_modules/express\0", 0x7FFF5FBFED08, 0x3)         = 0 0
643523 lstat64(".../node_modules/express/index.js\0", 0x7FFF5FBFED08, 0x3)        = 0 0
643598 open(".../node_modules/express/index.js\0", 0x0, 0x1B6)        = 12 0
643600 fstat64(0xC, 0x7FFF5FBFED58, 0x1B6)         = 0 0

Mission achieved. Note that the speedup only happens after the first application run finishes successfully. The resolution cache needs to be saved to a local file, and this happens only on process exit.

Small print

Author: Gleb Bahmutov © 2015

License: MIT - do anything with the code, but don't blame me if it does not work.

Spread the word: tweet, star on github, etc.

Support: if you find any problems with this module, email / tweet / open issue on Github

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