RingoJS

Modules in Ringo

Ringo implements the CommonJS Modules specification. In short this means:

The CommonJS module specification is also the foundation behind Node's module system, so for Node developers modules in Ringo are quite familiar.

Anatomy of a module

In Ringo every JavaScript file is treated as a module. When a module is executed, Ringo provides it with the means to import functionality from and export functionality to other modules.

An example should make things clearer. A simple module in the file simplemath.js might look like the following. It exposes the function add, but not the private adder function:

// simplemath.js
var adder = function(a, b) {
    return a + b;
};
exports.add = function(a, b) {
    return adder(a, b);
};

You can require() it and then access add as simplemath.add():

>> var simplemath = require('./simplemath');
>> simplemath.add(3,4)
7

But you can not access the private "adder" function:

>> simplemath.adder(2,2)
ReferenceError

Ringo also provides a module object to each module with the following properties:

Modules are executed in their own private scope. Thus, everything defined in a module, which is not explicitly exported, is private to the module and invisible to other modules. Variables (unintentionally) declared without var will be only global to the module. This keeps the global scope isolated from the potential module scope leaks. The global object is accessible through the implicit global variable. Good application design avoids the global variable! Otherwise shared global state is introduced, which is a fundamental anti-pattern in Ringo.

Module identifiers

The string that identifies a module is called a module id.

The module id corresponds to the file name of the module with the .js extension omitted.

Module ids starting with './' or '../' are called relative ids. Relative ids are looked up relative to the location of the current module following common file system semantics.

A module id not starting with './' or '../' is called an absolute id and is resolved against the module path.

The module path

The module path is a list of standard locations in which Ringo will look for modules.

The module path can be set in the following ways:

Packages

Note: rp and ringo-admin are two package management tools for Ringo.

Packages provide a means of bundling several modules and other resources into one unit. Packages are directories that contain a package.json package descriptor file. The main property in the package.json descriptor is recognized by Ringo's module loader as the main entry point for a module:

{
    "main": "lib/main.js"
}

If a module id resolves directly to a package directory and package.json defines a main property, Ringo will try to load the specified resource. The value of the main property must be a path relative to the package root.

If a module id resolves to a directory that does not contain a package.json file, or package.json does not define a main property, Ringo will try to load file index.js in that directory.

If part of a module id resolves to a package directory, Ringo will try to resolve the remaining part of the id against the lib directory of that package. The location of the lib directory can be overridden using the directories.lib property in package.json.

{
    "directories": {
        "lib": "new-lib"
    }
}

Caching and reloading

Modules are cached after they are loaded for the first time. Ringo tries to resolve module ids to a canonical path in order to not load the same module twice, but it is possible under rare circumstances that this fails and a module is loaded twice.

By default, Ringo's module loader checks if the module or any module it depends on has changed each time it is required. If so, the module is loaded again.

To disable module reloading run ringo with the -p or --production option, or set the production servlet init parameter to true.

Ringo module extensions

The CommonJS modules specification was kept deliberately small. Ringo provides some extra niceties for exporting and importing stuff. The downside to using these is that your code is tied to Ringo, but it's relatively easy to convert the code to "pure" CommonJS, and there's also a command line tool for that purpose.

One Ringo extension is the include function. This is similar to require, but instead of returning the other module's exports object as a whole it directly copies each of its properties to the calling module's scope, making them usable like they were locally defined.

include is great for shell work and quick scripts where typing economy is paramount, and that's what it's meant for. It's usually not a great idea to use it for large, long lived programs as it conceals the origin of top-level functions used in the program.

For this purpose, it's more advisable to use require in combination with JavaScript 1.8 destructuring assignment to explicitly include selected properties from another module in the local scope:

var {foo, bar} = require("some/module");

The above statements imports the "foo" and "bar" properties of the API exported by "some/module" directly in the calling scope.

On the exporting side, Ringo provides an export function that takes a variable number of local variable names to be exported from the current module. Internally, this just copies the given variables to the module's exports object, so it's just a way to keep a module's exports in one place.

export("foo", "bar", "baz");