1.2.8 • Public • Published


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A pattern for writing concise and testable Javascript classes.

Definite supports mixins that can add option immutability, call stack graphing, and more.

Eliminate vague variables

First let's look at what its like to require and use a definite class:

import thing from "./thing"
thing() // new instance of Thing!

Why is this cool? Because when you call the function again, it returns the same instance:

import thing from "./thing"
thing() // new instance
thing() // same instance!

Everywhere you see thing, you know exactly what it is.

You can create multiple instances using a key:

import thing from "./thing"
thing("a") // new instance of Thing "a"
thing("a") // same instance of Thing "a"
thing("b") // new instance of Thing "b"
thing("b") // same instance of Thing "b"

One options API to rule them all

Classes can receive options as well:

import thing from "./thing"
thing({ hello: "world" }) // new instance with options
thing({ hello: "me" })    // update instance with options

And yes, options work with keys:

import thing from "./thing"
thing("a", { hello: "world" }) // new "a" instance with options
thing("a", { hello: "me" })    // update "b" instance with options

Do one thing and do it well

Introducing then:

import thing from "./thing"
thing().then() // do the thing

Think of then as the single entry point to executing any post-initialization logic.

And oh yeah, its chainable:

import thing from "./thing"
import otherThing from "./other-thing"
thing().then(otherThing(), () => {
  console.log("did all the things!")

Above we passed multiple thenable parameters to then to automatically chain them.

Thenable parameters can be promises, functions, or other definite classes.

How to define a class

Let's look at how we define a skeleton definite class:

// skeleton.js
import def from "definite"
export default def(class {
  constructor(options) {} // initialize options
  set(options) {}         // update options
  then(...args) {}        // returns definite instance, promise, or value

Now let's use the class we made:

import skeleton from "./skeleton"
skeleton({ a: true })  // calls `constructor(options)`
skeleton({ a: false }) // calls `set(options)`
skeleton().then()      // calls `then()`

Dependency autoloading

Its easy to autoload other definite classes in your project.

Configure a definite builder:

// lib/component.js
import definite from "definite"
export default definite({
  autoload: [

And use it in your classes:

// components/hello.js
import component from "../lib/component"
class Hello {
  constructor() {
    this.components.thing()  // new instance of `components/thing`
    this.models.otherThing() // new instance of `models/other-thing`
export default component(Hello)


Its easy to extend your definite classes:

// lib/component.js
import def from "definite"
let mixin = (Extend) =>
  class extends Extend {
    constructor(options) {
    set(options) {
    then(...args) {
      return super(...args)
export default def({
  mixins: [ mixin ]

Then use it to define your classes:

// components/hello.js
import component from "../lib/component"
class Hello {
  constructor() {}
  set(options) {}
  then(...args) {}
export default component(Hello)

Definite runner

The def command automatically requires your definite class and executes then on it:

def path/to/class -o "{ option: true }"

Use -o to specify options to pass into the class constructor.




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