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install

Minimal JavaScript module loader

install

The CommonJS module syntax is one of the most widely accepted conventions in the JavaScript ecosystem. Everyone seems to agree that require and exports are a reasonable way of expressing module dependencies and interfaces, and the tools for managing modular code are getting better all the time.

Much less of a consensus has developed around the best way to deliver CommonJS modules to a web browser, where the synchronous semantics of require pose a non-trivial implementation challenge. This module loader contributes to that confusion, yet also demonstrates that an amply-featured module loader need not stretch into the hundreds or thousands of lines.

From NPM:

npm install install

From GitHub:

cd path/to/node_modules
git clone git://github.com/benjamn/install.git
cd install
npm install .

The first step is to create an install function by calling the makeInstaller method. Note that all of the options described below are optional:

var install = require("install").makeInstaller({
  // Optional list of file extensions to be appended to required module 
  // identifiers if they do not exactly match an installed module. 
  extensions: [".js", ".json"],
 
  // If defined, the options.onInstall function will be called any time 
  // new modules are installed. 
  onInstall,
 
  // If defined, the options.override function will be called before 
  // looking up any top-level package identifiers in node_modules 
  // directories. It can return either a string to provide an alternate 
  // package identifier or a non-string value to prevent the lookup from 
  // proceeding. 
  override,
 
  // If defined, the options.fallback function will be called when no 
  // installed module is found for a required module identifier. Often 
  // options.fallback will be implemented in terms of the native Node 
  // require function, which has the ability to load binary modules. 
  fallback
});

The second step is to install some modules by passing a nested tree of objects and functions to the install function:

var require = install({
  "main.js": function (require, exports, module) {
    // On the client, the "assert" module should be install-ed just like 
    // any other module. On the server, since "assert" is a built-in Node 
    // module, it may make sense to let the options.fallback function 
    // handle such requirements. Both ways work equally well. 
    var assert = require("assert");
 
    assert.strictEqual(
      // This require function uses the same lookup rules as Node, so it 
      // will find "package" in the "node_modules" directory below. 
      require("package").name,
      "/node_modules/package/entry.js"
    );
 
    exports.name = module.id;
  },
 
  node_modules: {
    package: {
      // If package.json is not defined, a module called "index.js" will 
      // be used as the main entry point for the package. Otherwise the 
      // exports.main property will identify the entry point. 
      "package.json": function (require, exports, module) {
        exports.name = "package";
        exports.version = "0.1.0";
        exports.main = "entry.js";
      },
 
      "entry.js": function (require, exports, module) {
        exports.name = module.id;
      }
    }
  }
});

Note that the install function merely installs modules without evaluating them, so the third and final step is to require any entry point modules that you wish to evaluate:

console.log(require("./main").name);
// => "/main.js" 

This is the "root" require function returned by the install function. If you're using the install package in a CommonJS environment like Node, be careful that you don't overwrite the require function provided by that system.

Many more examples of how to use the install package can be found in the tests.