A lightweight & asynchronous JavaScript loader for CommonJS and NodeJS modules.
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Important notice: Tarp.require is the replacement of Smoothie. It introduces a number of new features and improvements, so it is recommended to use Tarp.require from now on. Please read the migration documentation for further information.

//\ Tarp.require - a lightweight JavaScript module loader

Tarp.require is a CommonJS and Node.js compatible module loader licensed as open source under the LGPL v3. It aims to be as lightweight as possible while not missing any features.

Tarp.require has finally reached a stable state. This means that the version 1.x branch will only receive bugfixes from now on. An improved version of Tarp.require with new features and breaking changes can be found in the tarp2-branch.


  • Compatible NodeJS 9.2.0 and CommonJS modules 1.1
  • Plain No dependencies, no need to compile/bundle/etc the modules
  • Asynchronous Non-blocking loading of module files
  • Modern Makes use of promises and other features (support for older browsers via polyfills)
  • Lightweight Just about 180 lines of code (incl. comments), minified version is about 2kB

Browser compatibility


The easiest way to install Tarp.require is via NPM:

$ npm install --save @tarp/require

If you don't want to use NPM you can just clone the repository directly or add it to your git repository as a submodule:

$ git submodule add https://github.com/letorbi/tarp.require.git


Assuming you've installed Tarp.require in the folder //example.com/node_modules/@tarp/require and your HTML-document is located at //example.com/page/index.html, you only have to add the following lines to your HTML to load the script located at //example.com/page/scripts/main.js as your main-module:

<script src="/node_modules/@tarp/require/require.min.js"></script>
<script>Tarp.require({main: "./scripts/main"});</script>

Inside your main-module (and any sub-module, of course) you can use require() as you know it from CommonJS/NodeJS. Assuming you're in the main-module, module-IDs will be resolved to the following paths:

  • require("someModule") loads //example.com/page/node_modules/someModule.js
  • require("./someModule") loads //example.com/page/scripts/someModule.js
  • require("/someModule") loads //example.com/someModule.js

Note that global modules are loaded from //example.com/page/node_modules and not from //example.com/node_modules. This is because the default global module path is set to ['./node_modules'] and is derived from the location of the page that initializes Tarp.require.

Synchronous and asynchronous loading

Tarp.require supports synchronous and asynchronous loading of modules. If you load Tarp.require like described above and use only simple require calls you won't have to care about anything: Just write require("someModule") and Tarp.require will try to load the module and all its sub-modules asynchronously.

However, there might be occasions where you have to force Tarp.require to load a module synchronously. This is possible, but you should try to avoid this, because synchronous requests might block the loading process of your page and are therefore marked as obsolete by now.

Keep also in mind that synchronous loading of a module prevents the pre-loading of its sub-modules. You have to explicitly load a sub-module asynchronously to re-start the pre-loading.

What modules can be pre-loaded?

Right now only plain require-calls are pre-loaded. This means that the ID of the module has to be one simple string. Also require-calls with more than one parameter are ignored.

Example: If a module has been loaded asynchronously and contains the require calls require("Submodule1"), require("Submodule2", true) and require("Submodule" + "3") somewhere in its code, only Submodule1 will be pre-loaded, since the require-call for Submodule2 has more than one parameter and the module-ID in the require-call for Submodule3 is not one simple string.

Enforce synchronous or asynchronous loading

Synchronous or asynchronous loading of a module can be enforced by adding a boolean value as a second parameter to the require-call:

// explicit synchronous loading
var someModule = require("someModule", false);

 // explicit asynchronous loading
require("anotherModule", true).then(function(anotherModule) {

Path resolving

Tarp.require mainly resolves URLs in the same way as Node.js does resolve paths. The only difference is that Tarp.require won't look for a file at other locations if it cannot be found at the resolved URL. This decision has been made due to the fact that modules are usually loaded from a remote server and sending multiple request for different locations would be very time-consuming. Tarp.require relies on the server to resolve unknown files instead.

HTTP redirects

Tarp.require is able to handle temporary (301) and permanent (303) HTTP redirects. A common case where redirects might be handy is to return the contents of index.js or package.json if an ID without a filename is requested. The following NGINX configuration rule will mimic the behavior of NodeJS:

location /node_modules {
    if ( -f $request_filename ) {
    if ( -f "${request_filename}package.json" ) {
        return 301 "${request_uri}package.json";
    if ( -f "${request_filename}index.js" ) {
        return 301 "${request_uri}index.js";
    return 404;

This will redirect all requests like /node_modules/someModule to /node_modules/someModule/package.json, if /node_modules/someModule is a directory and if /node_modules/someModule/package.json is a file. If that file doesn't exist, the request will be redirected to /node_modules/path/index.js. If both files don't exist, a "404 Not Found" response will be sent.

Note: HTTP redirects won't work in IE11 due to limited support of XMLHttpRequest advanced features.

NPM packages

// The loading of a NPM package is the only occasion when Tarp.require might redirect a request on its own. Tarp.require load a module-ID specified the main field of a package.json file, if the following checks are true:

  1. The package.json file is loaded via a redirect (like explained in the section above)
  2. The response contains a valid JSON object
  3. The object has a property called main

If that is the case a second request will be triggered to load the modules specified in main and the exports of that module will be returned. Otherwise simply the content of package.json is returned.

The module.paths property

Tarp.require always uses the first item of the global paths array to resolve an URL from a global module-ID. Unlike Node.js it won't iterate over the whole array. Since the global config is always used, any change to module.paths won't affect the loading of modules.

Tarp.require also supports the require.resolve.paths() function that returns an array of paths that have been searched to resolve the given module-ID.


Change the global module path

If your modules are not located at ./node_modules/, you can tell Tarp.require their location via the paths option:

Tarp.require({main: "./scripts/main", paths: ["/path/to/node/modules"]});

Override path resolver

If you need a more sophisticated path resolver, you can override the default function that resolves a module-id to the according URL:

Tarp.require({main: "./scripts/main", resolver: function(id, pwd, resolve) { ... }});

The parameter id is the module-id of the module that shall be loaded, pwd is the path of the module require() is called from and resolve points to the build-in path-resolver function (you might want to call this).

Keep in mind that a custom path-resolver may break NodeJS or CommonJS compatibility, if not implemented properly.

Change the document root path

The document root path is used to resolve relative paths inside the paths array. It points to location.href by default. You have to set the document root path explicitly, if you want to use Tarp.require inside a web-worker that has been loaded from a blob.

Tarp.require({main: "./scripts/main", root: "/path/to/page/"});

Using require() directly in the HTML-document

It is not recommended to load other modules than the main-module directly from your HTML-document. However, if you really want to use require() directly in the HTML-document, you can add Tarp.require to the global scope:

Tarp.require({expose: true});

Keep in mind that a require-call in the HTML-document will load a module synchronously unless you explicitly load it asynchronously by adding true as a second parameter.

Load the main-module synchronously

If you really need to load the main-module synchronously, you can do it by loading Tarp.require with the following options:

Tarp.require({main: "./scripts/main", sync: true});

Copyright 2013-2018 Torben Haase <https://pixelsvsbytes.com>