Workflow

Workflows represent the various states and transitions that an entity can go through in a system. For example, let's say you're developing a task management application. You'll need to establish some rules:

• When a user creates a task, does it start as new?
• Can a task move directly from in progress to completed, or does it need to be reviewed first?
• You might allow deleting new tasks, but should completed tasks only be archived?

These kinds of questions can be tricky, and it's crucial to represent this logic clearly in your code.

Install

npm i @jean-michelet/workflow

Workflow

The Workflow class lets you define state transitions and apply them to the state property of an entity. You can define transitions from a single state or from multiple states.

In this example, a task can move through several stages in its lifecycle: from new to in progress, then either to completed or canceled, and finally be archived from either the canceled or completed states:

// Example in typecript, but also works with vanilla JS
import {
  Transition,
  MultiOriginTransition,
  Workflow,
} from "@jean-michelet/workflow";

class Task {
  status = "new";
}

const workflow = new Workflow<Task>({
  stateProperty: "status",
});

workflow.addTransition("start", new Transition("new", "in progress"));
workflow.addTransition("complete", new Transition("in progress", "completed"));
workflow.addTransition("cancel", new Transition("in progress", "canceled"));
workflow.addTransition(
  "archive",
  new MultiOriginTransition(["canceled", "completed"], "archived")
);

const task = new Task();

if (workflow.can("start", task)) {
  workflow.apply("start", task);
}
console.log(task.status); // Output: "in progress"

if (workflow.can("cancel", task)) {
  workflow.apply("cancel", task);
}
console.log(task.status); // Output: "canceled"

if (workflow.can("archive", task)) {
  workflow.apply("archive", task);
}
console.log(task.status); // Output: "archived"

Handling Unexpected States

The Workflow class supports a detectUnexpectedState option. When enabled, this option throws an error if an entity is in an unexpected state that hasn't been accounted for in the defined transitions:

// Example in typecript, but also works with vanilla JS
import { Workflow, Transition } from "@jean-michelet/workflow";

class Task {
  status = "unknown";
}

const workflow = new Workflow<Task>({
  stateProperty: "status",
  detectUnexpectedState: true,
});

workflow.addTransition("start", new Transition("new", "in progress"));

const task = new Task();

workflow.can("start", task); // Error: "The instance has an unexpected state 'unknown'"