fount

Fount

Fount is a promise based DI container for Node.js.

Getting started

npm install fount -S

var fount = require( 'fount' );

A note about style and safety

Fount supports two styles of identifying dependency: string array (like AMD) and by argument names (like Angular).

Example:

// string array
fount.inject( [ 'one', 'two', 'three' ], function( one, two, three ) {
	// your code here
} );

// argument name
fount.inject( function( one, two, three ) {
	// your code here
} );

The second approach is easier to read when starting out, but consider how fragile it is. If someone were to come along and refactor your generic arguments to be more expressive and not change the keys the dependencies were registered against, it would break a lot of code.

You get to choose the style you prefer, just keep in mind there's more risk with argument name only.

Multiple Containers

Fount supports multiple containers. If you don't specify one when making calls, it will use the 'default' container. Most examples in this doc use the default container implicitly.

You can use a named container in two ways:

• pass the container name in parenthesis before making the call (all commands)
• use period delimited namespaces in your key names (all commands except purge)

fount( 'myContainer' ).resolve( 'myKey' ).then( function( value ) { 
	// do something cool
} );

// same as above, but terser
fount.resolve( 'myContainer.myKey' ).then( function( value ) { 
	// do something cool
} );

Scope & Lifecycles

Chances are you won't need this - you'll register dependencies and resolve them and never think about lifecycle or scope. When you do need more control, fount allows you to supply lifecycle arguments during registration and an optional scope name during resolution that give you more granular control over resolution.

Scope

A scope is just a simple name that can affect how a function dependency is resolved if it was specified with a scoped lifecycle. When resolving a dependency with a scoped lifecycle, a default will be used when resolving dependencies. (see the Registering section for examples)

Think of a scope in Fount like a second level of caching (because that's exactly what it is). You can purge a scope anytime with purgeScope:

fount.purgeScope( 'myScope' );

Lifecycle ( static, scoped or factory )

A lifecycle tells fount how long the result of a function dependency is good for. Static is the the default.

• static - once a value is returned, it will always be returned for future resolution
• scoped - like static but resolved once per scope (specified by name)
• factory - if the dependency is a function it will re-evaluated every time

Registering

Registering is simple - provide a string name and then supply either a value, function or promise. See each section for more detail.

// lifeCycle is optional and 'static' by default
fount.register( 'name', value | function | promise, [lifeCycle] );

value

Once a value is registered, fount will always supply that value to any resolve call. It doesn't actually make sense to provide a lifecycle option with a value or promise since it has no effect, but fount doesn't freak out if you forget and do this by accident.

fount.register( 'port', 8080 );

function

Registering a function with fount will cause it to invoke the function during resolution and return the result.

fount.register( 'factory', function() { return 'a thing!' } );

Registering functions with dependencies

If you want fount to inject dependencies into the function when calling it, you'll need to provide a string array of the dependencies in the order they should be supplied to the function:

// AMD users should feel right at home with this style
fount.register( 'factory', [ 'a', 'b', 'c' ], function( a, b, c ) {} );

// Angular fans and dare-devils may enjoy this style
// dependencies are 'read' out of the argument list
fount.register( 'factory', function( a, b, c ) {} );

Registering functions as values

You may want to register a function as a value (confused yet?) so that fount returns the function as a dependency rather than executing it for you. If that's what you're looking for, try this:

fount.register( 'calculator', function() { return function( x, y ) { return x + y; }; } );

promise

Registering a promise looks almost identical to registering a function. From a consuming perspective, they're functionally equivalent since fount will wrap raw function execution in a promise anyway.

fount.register( 'todo', when.promise( function( reject, resolve ) {
	resolve( 'done' );
} ) );

Resolving

Resolving is pretty simple - fount will always return a promise to any request for a dependency.

fount.resolve( 'gimme' ).then( function( value ) { // do something } );

fount.resolve( 'gimme', 'custom' ).then( function( value ) { // value for scope 'custom' } );

// resolve multiple dependencies at once!
fount.resolve( [ 'one', 'two' ] ).then( function( results ) {
	// results is a hash, not an array
} );

// resolve multiple dependencies ACROSS containers
fount.resolve( [ 'a.one', 'b.two' ] ).then( function( results ) {
	// results is a hash, not an array
} );

Injecting

Injecting is how you get fount to invoke a function on your behalf with resolved dependencies. If you're familiar with AMD, it's somewhat similar to how define works.

// where 'a' and 'b' have been registered
fount.inject( [ 'a', 'b' ], function( a, b )  { ... } );

// within custom scope -- requires a and/or b to have been registered with 'scoped' lifecycle
fount.inject( [ 'a', 'b' ], function( a, b )  { ... }, 'myScope' );

// using keys across multiple containers
fount.inject( [ 'one.a', 'two.b' ], function( a, b ) { ... } );

Diagnostic

Right now this is pretty weak, but if you call log, Fount will dump the containers and scopes out so you can see what keys are present. Got ideas for more useful ways to troubleshoot? I'd love a PR :smile:!

Things to do soon

• Good error handling - returning clear error messages when a resolution/injection fails