ts-fp-di

Tiny TypeScript functional dependency injection, based on Node.js AsyncLocalStorage.

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Firstly, need init DI container for each life cycle of your backend application (each HTTP request/response, handle MQ message, ...).

Example of middleware for typical Koa application, where on each HTTP request will be created particular DI container:

app.use(async (ctx, next) => {
  await diInit(async () => return await next());
});

Further, simply use ts-fp-di API "as is" in code, it will consider particular DI scope.

Examples

Basic

const fn = di(() => 1);
fn() // call `fn` function inside DI scope, it's return 1

Override dependency (method 1)

const fn = di(() => 1);
diSet(fn, () => 2); // Override `fn` function inside DI scope. Useful for unit tests.
fn() // returns 2, because it rewriten.

Override dependency (method 2)

const fn = () => 1;
diSet(fn, () => 2); // Override `fn` function inside DI scope. Useful for unit tests.
diDep(fn)() // returns 2, because it rewriten.

Dependency by string key

diSet('user', {login: 'xxx'}); // Useful to setup current user in DI scope
diDep<User>('user') // Extract current user from anywhere

State managment in DI scope

// setup Redux like state with reducer in DI scope
const inc = dis((sum, n: number) => sum + n, 0); 
inc(1); // mutate state
inc(); // 1, "inc" without argument returns current state

State managment in global scope

// setup Redux like state with reducer in global scope (pass true as isGlobal flag)
const inc = dis((sum, n: number) => sum + n, 0, true); 
inc(1); // mutate state
inc(); // 1, "inc" without argument returns current state

clearGlobalState(); // you can clear global state (useful in tests)
inc() // 0, "inc" returns default value now

Singleton for DI scope

let i = 0;
const fn = diOnce(() => { // <- setup Singleton function for DI scope
  i += 1;
  return i;
});

fn(); // 1
fn(); // also 1, because fn is singleton for DI scope

Singleton constant for DI scope

const cache = dic<number>()

cache(1)
cache() // 1

Override Singleton for DI scope

const fn = diOnce((n: number) => { // <- setup Singleton function for DI scope
  return n + 1;
});

diOnceSet(fn, -1); // Override diOnceSet. For example, use this in your unit tests
fn(4) // -1 instead 5, because -1 set on prev line

Check that runtime in DI scope

diExists() // false

diInit(() => {
  diExists() // true
});

Share DI context

const ctx = diContext()

diInit(() => {
  // ctx will be considered here
}, ctx)

diInit(() => {
  // same ctx will be considered here too
}, ctx)

DI Scope (OOP incapsulation alternative)

const inc = dis((resp: number, n: number) => resp + n, 0)

const scope = diScope({ inc }, () => {
  // optional "constructor" function
  // some `diSet` can be used here
})

scope.inc(5) // this mutation occur only inside this scope
scope.inc() // 5 

Functional reactive programming, mapping

const cacheNumber = dic<number>()
const calcString = diMap(n => `string - ${n}`, cacheNumber)

cacheNumber(5)
calcString() // "string - 5"

const onceNumber = diOnce((n: number) => {
  return n;
});
const calcString = diMap(n => `string - ${n}`, onceNumber)

onceNumber(5)
calcString() // "string - 5"

const inc = dis((sum, n: number) => sum + n, 0);
const calcString = diMap(s => `string - ${s}`, inc)
inc(1);
inc(4);
calcString() // "string - 5"

calcString.raw(1) // direct call of function, useful for unit tests

const cacheNumber = dic<number>()
let i = 0
const onceString = diMapOnce(n => ((i = i + 1), `string - ${n}`), cacheNumber)

cacheNumber(5)
onceString() // "string - 5"
onceString() // i = 1, because onceString is singleton for DI scope

Attach async effect to State

const numberState = dic<number>()
const stringState = diMap(n => `string - ${n}`, numberState)
const seState = dic<string>() // will be populated via side effect
const se = dise(
  async (n, s) => `${n} ${s}`, // side effect async function
  seState, // this state will be populated via async response
  n, // optional arg1 for effect function
  s) // optional arg2 for effect function

await se()

seState() // "5 string - 5"

Plugins

Internal AsyncLocalStorage instance exposed as als property. You can implement your own plugin around it.

‼️ If you use ts-fp-di with plugins on your project, please consider, that you have only one ts-fp-di node_module For example you can freeze as singleton you dependency via package.json overrides

{
  "overrides": {
    "ts-fp-di": "^x.x.x"
  }
}

• ts-fp-di-mikroorm - Use MikroORM Entities inside ts-fp-di State and achieve auto persistence in DB
• ts-fp-di-rxjs - Utils for RxJS for working with ts-fp-di
• rxjs-wait-next - Wait RxJS Subject.next emition for all subscribers