FlowJS

A simple in-memory framework for creating workflows in JS.

Very much WIP. Tests incoming.

Flows

A workflow or Flow is a composition of Activities that are executed sequentially, with a Decider determining the next Activity upon completion. The Context represents the state of the workflow and is the only stateful component. The Decider depends solely on the Context to determine the next activity - in the example we simply map the flow states to different activities.

A workflow is composed of four implementation-specific components:

• Decider
• Context
• A set of logical workflow states
• A set of Activities

And a Flow executor that steps through the workflow and handles exceptions.

Workflow States

The Flow executor expects a map of Symbols that represent the possible states in the workflow. Two default states must exists: START and END.

    var flowStates = {
        START : Symbol("START"),
        A : Symbol("A"),
        B : Symbol("B"),
        END : Symbol("END")
    }

Activities

At the core of the workflow, are Activities. Each Activity is single logical step in the workflow and is ideally idempotent. Activities are stateless, they are passed the workflow's Context during execution. To pass state between activities, subclass the context for your workflow to set/get state.

The Activity class only has two properties:

• Name, and
• A function that accepts a context and executes the activity's business logic.

Note: Currently, the activity is responsible for setting the next state. The core logic in the Flow will retry activites that throw exceptions if the instanceof RetryableException => true.

Example:

  var ActivityA = new Activity("ActivityA", function (context) {
      console.log("Executing ActivityA");
      context.setState(context._states.B);
  });

  var ActivityB = new Activity("ActivityB", function (context) {
      console.log("Executing ActivityB");
      // Will retry until it exhausts attempts
      throw new RetryableException();
      context.setState(context._states.END);
  });

Decider

The Decider is responsible for taking a context and returning the next Activity to execute. Note in the example, we define a starting activity -- this is required at the moment.

Example:

    var decider = new Decider(function(context){
        switch(context.getState()) {
            case flowStates.START: return ActivityA;
            case flowStates.A: return ActivityA;
            case flowStates.B: return ActivityB;
        }
    });

Debug

Set DEBUG=flowjs:* to get debug output.

Events

• success (Flow)
• failure (Flow)
• complete (Flow)
• error (Error, Flow)