jpex

Easy Dependency Injection

Jpex is an Inversion of Control framework. Register dependencies on a container, then resolve them anywhere in your application. The real magic of jpex is its ability to infer dependencies using the magic of babel and typescript...

Contents

• Getting Started
• Registering Dependencies
• Consuming Dependencies
• API
  • jpex
  • types
• caveats
• react
• Vanilla JS mode

Getting Started

Install

npm install jpex

Plugin

Jpex uses babel to infer type interfaces at build time. You can do this with one of several methods: @jpex-js/babel-plugin @jpex-js/rollup-plugin @jpex-js/webpack-plugin

Jpex comes bundled with the @jpex-js/babel-plugin so you can easily get started with a .babelrc like this:

// .bablerc
{
  presets: [ '@babel/preset-typescript' ],
  plugins: [ 'jpex/babel-plugin' ]
}

Usage

import jpex from 'jpex';
import { IFoo, IBah } from './types';

jpex.factory<IFoo>((bah: IBah) => bah.baz);

const foo = jpex.resolve<IFoo>();

---

Registering Dependencies

Services and factories are small modules or functions that provide a reusable or common piece of functionality.

factories

type MyFactory = {};

jpex.factory<MyFactory>(() => {
  return {};
});

services

type MyService = { method: () => any };

jpex.service<MyService>(function(){
  this.method = function(){
    ...
  };
});

constants

type MyConstant = string;
jpex.constant<MyConstant>('foo');

---

Consuming Dependencies

resolve

You can then resolve a dependency anywhere in your app:

const value = jpex.resolve<MyFactory>();

dependent factories

You can also request a dependency from within another factory:

jpex.constant<MyConstant>('foo');

jpex.factory<MyFactory>((myConstant: MyConstant) => {
  return `my constant is ${myConstant}`;
});

encase

Or you can encase a function so that dependencies are injected into it on-the-fly:

const myFn = jpex.encase((value: MyFactory) => (arg1, arg2) => {
  return value + arg1 + arg2;
});

---

API

jpex

jpex.constant

<T>(obj: T): void

Registers a constant value.

jpex.factory

<T>(fn: (...deps: any[] => T), opts?: object): void

Registers a factory function against the given type. Jpex works out the types of deps and injects them at resolution time, then returns the resulting value T.

type GetStuff = () => Promise<string>;

jpex.factory<GetStuff>((window: Window) => () => window.fetch('/stuff));

The following options can be provided for both factories and services:

lifecycle

'application' | 'class' | 'instance' | 'none'

Determines how long the factory is cached for once resolved.

• application is resolved forever across all containers
• class is resolved for the current jpex container, if you .extend() the new container will resolve it again
• instance if you request the same dependency multiple times in the same resolve call, this will use the same value, but the next time you call resolve it will start again
• none never caches anything

The default lifecycle is class

precedence

'active' | 'passive'

Determines the behavior when the same factory is registered multiple times.

• active overwrites the existing factory
• passive prefers the existing factory

Defaults to active

bindToInstance

boolean

Specifically for services, automatically binds all of the dependencies to the service instance.

jpex.service

<T>(class: ClassWithConstructor, opts?: object): void

Registers a service. A service is like a factory but instantiates a class instead.

class Foo {
  constructor(window: Window) {
    // ...
  }
}

jpex.service<Foo>(Foo);

jpex.alias

<T>(alias: string): void

Creates an alias to another factory

jpex.resolve

<T>(opts?: object): T

Locates and resolves the desired factory.

const foo = jpex.resolve<Foo>();

The following options can be provided for both resolve and resolveWith:

optional

boolean

When true if the dependency cannot be found or resolved, it will just return undefined rather than throwing an error.

with

object

Lets you pass in static values to use when resolving dependencies. This should be used as an escape hatch, as resolveWith was created specifically for this purpose.

jpex.resolveWith

<T, ...Rest[]>(values: Rest, opts?: object): T

Resolves a factory while substituting dependencies for the given values

const foo = jpex.resolveWith<Foo, Bah, Baz>([ 'bah', 'baz' ]);

jpex.encase

(...deps: any[]): (...args: any[]) => any

Wraps a function and injects values into it, it then returns the inner function for use.

const getStuff = jpex.encase((http: Http) => (thing: string) => {
  return http(`api/app/${thing}`);
});

await getStuff('my-thing');

To help with testing, the returned function also has an encased property containng the outer function

getStuff.encased(fakeHttp)('my-thing');

jpex.extend

(config?: object): Jpex

creates a new container, using the current one as a base.

This is useful for creating isolated contexts or not poluting the global container.

The default behavior is to pass down all config options and factories to the new container.

inherit

boolean

Whether or not to inherit config and factories from its parent

lifecycle

'application' | 'class' | 'instance' | 'none'

The default lifecycle for factories. class by default

precedence

'active' | 'passive'

The default precedence for factories. active by default

optional

boolean

Whether factories should be optional by default

nodeModules

boolean

When trying to resolve a tdependency, should it attempt to import the dependency from node modules?

globals

boolean

When trying to resolve a dependency, should it check for it on the global object?

jpex.raw

<T>() => (...deps: any[]) => T

Returns the raw factory function, useful for testing.

jpex.clearCache

() => void
<T>() => void

Clears the cache of resolved factories. If you provide a type, that specific factory will be cleared, otherwise it will clear all factories.

jpex.infer

<T>() => string

Under the hood jpex converts types into strings for runtime resolution. If you want to get that calculated string for whatever reason, you can use jpex.infer

Types

Jpex

This is the type definition for the jpex container

NodeModule

This is a special type that lets you automatically inject a node module with type inference.

For example:

import jpex, { NodeModule } from 'jpex';

// this will resolve to the fs module without you having to explicitly register it as a dependency
const fs = jpex.resolve<NodeModule<'fs'>>();

The default return type will be any but you can specify one explicitly with the second type parameter:

import type fstype from 'fs';
import jpex, { NodeModule } from 'jpex';

const fs = jpex.resolve<NodeModule<'fs', typeof fstype>>();

Global

This is another special type that lets you automatically inject a global property with type inference.

For built-in types you can do this without any helpers:

import jpex from 'jpex';

const navigator = jpex.resolve<Navigator>();

But for custom globals, or properties that don't have built-in types, you can use the Global type:

import jpex, { Global } from 'jpex';

const analytics = jpex.resolve<Global<'ga', Function>>();

caveats

There are a few caveats to be aware of:

• Only named types/interfaces are supported so you can't do jpex.factory<{}>()
• There is not yet a concept of extending types, so if you do interface Bah extends Foo {} you can't then try to resolve Foo and expect to be given Bah, they are treated as 2 separate things
• The check for a jpex instance is based on the variable name, so you can't do const jpex2 = jpex; jpex2.constant<Foo>(foo); without explicitly adding jpex2 to the plugin config
• Similiarly you can't do const { factory } = jpex

react

Jpex is a really good fit with React as it offers a good way to inject impure effects into pure components. There is a react-jpex library that exposes a few hooks.

import React from 'react';
import { useResolve } from 'react-jpex';
import { SaveData } from '../types';

const MyComponent = (props) => {
  const saveData = useResolve<SaveData>();

  const onSubmit = () => saveData(props.values);

  return (
    <div>
      <MyForm/>
      <button onClick={onSubmit}>Submit</button>
    </div>
  );
};

And this pattern also makes it really easy to isolate a component from its side effects when writing tests:

import base, { Provider, useJpex } from 'jpex';
// create a stub for the SaveData dependency
const saveData = stub();
// create a new container
const jpex = base.extend();
// register our stub dependency
jpex.constant<SaveData>(saveData);

render(
  <Provider value={jpex}>
      {/* when we render MyComponent, it will be given our stubbed dependency */}
    <MyComponent/>
  </Provider>
);

// trigger the compnent's onClick
doOnClick();

expect(saveData.called).to.be.true;

Vanilla JS mode

Perhaps you hate typescript, or babel, or both. Or perhaps you don't have the luxury of a build pipeline in your application. That's fine because jpex supports vanilla js as well, you just have to explicitly state your dependencies up front:

const { jpex } = require('jpex');

jpex.constant('foo', 'foo');
jpex.factory('bah', [ 'foo' ], (foo) => foo + 'bah');

const value = jpex.resolve('bah');

Jpex uses language features supported by the latest browsers, but if you need to support IE11 et al. you can import from 'jpex/dist/es5` (or create an alias in your build process)