@halfbit/di v1.1.0

DI.js

DI.js is a simple yet extensible parameter dependency injection written in vanilla Javascript.

Usage example

Providable resources are called Parameter, an evaluation context is called Context. A Context can evaluate either a parameter name or the function which it will try to provide with all its parameters. A most basic usage would look like this:

import di from 'di';

let context = new di.Context();
context.addParameter('dog', { name: "Wooffers", bark: console.log.bind(window, 'Woof!') });

// No need for ugly ['dependency', function (dependency) {}] syntax
// Outputs 'Woof!' on the console!
context.evaluate(dog => dog.bark());

Under the hood, DI.js uses the functions toString method and some RegExp trickery to parse out all parameters. It works with named, anonymous and arrow functions, and supports default as well as rest parameters.

A caveat is that parameters with functions with parameters themselves as default parameter will not work.

Typing and custom adapters

DI.js offers type conversion via Adapters. An example would look like this:

context.addAdapter('json', JSON.stringify);

// Returns '{"name":"Woofers"}'
context.evaluate("dog_json");

An Adapter has a type that it produces and at least one transforming function.

It can also have multiple transforming functions for different input types:

context.addAdapter('str', String);
// Returns '[object Object]'
context.evaluate("dog_str");

// The third parameter is a fallback that is called if no matching input type is found
context.addAdapter('str', { 'object': JSON.stringify }, String);

// Returns '{"name":"Woofers"}'
context.evaluate("dog_str");

You might have noticed that the input type used here is 'object' and that we never provided a type together with the dog Parameter. We can actually specify our own type for Parameters to enable for even fancier Adapters:

context.addParameter('dog', { name: "Wooffers", bark: console.log.bind(window, 'Woof!') }, 'dog');
context.addParameter('neighboursCat', { name: "Spotty", meow: console.log.bind(window, 'meow~') }, 'cat');

context.addAdapter('call', { 'dog': d => d.bark, 'cat': c => c.meow });

// 'Woof!'
context.evaluate("dog_call")();
// 'meow~'
context.evaluate("neighboursCat_call")();

The default type name that is used if no type conversion is specified (f.i. context.evaluate('dog')) is 'def'. A newly created Context will always have an Adapter defined for this type that simply returns the value, i.e. a => a. However, if we override this Adapter then we can apply our own conversion, unbeknownst to the evaluated parameter or function:

context.addAdapter('def', { 'cat': a => a.name, 'dog': a => a.name }, a => a);

// 'Wooffers'
context.evaluate("dog");