AWS Local Step Functions

A Node.js implementation of the Amazon States Language specification.

This package lets you run AWS Step Functions locally on your machine!

NOTE: This is a work in progress. Some features defined in the specification might not be supported at all yet or might have limited support.

Features

To see a list of features that have full support, partial support, or no support, refer to this document.

Installation

npm install aws-local-stepfunctions

Importing

Currently, the only supported environment to import the package is Node.js. Browser support is not available yet.

Node.js

CommonJS

const { StateMachine } = require('aws-local-stepfunctions');

ES Module

import { StateMachine } from 'aws-local-stepfunctions';

API

Constructor: `new StateMachine(definition[, validationOptions])`

The constructor takes the following parameters:

definition: The Amazon States Language definition of the state machine.
validationOptions (optional): An object that specifies how the definition should be validated.
- checkPaths: If set to false, won't validate JSONPaths.
- checkArn: If set to false, won't validate ARN syntax in Task states.

The constructor will attempt to validate the definition by default, unless the validationOptions param is specified. If the definition is not valid, an error will be thrown.

Example:

import { StateMachine } from 'aws-local-stepfunctions';

const machineDefinition = {
  Comment: 'A simple minimal example of the States language',
  StartAt: 'Hello World',
  States: {
    'Hello World': {
      Type: 'Task',
      Resource: 'arn:aws:lambda:us-east-1:123456789012:function:HelloWorld',
      End: true,
    },
  },
};

// Instantiate a new state machine with the given definition and don't validate JSONPaths.
const stateMachine = new StateMachine(machineDefinition, { checkPaths: false });

`async StateMachine.run(input[, options])`

Executes the state machine with the given input parameter and returns the result of the execution.

It takes the following parameters:

input: The initial input to pass to the state machine. This can be any valid JSON value.
options (optional):
- overrides: An object to overrides the behavior of certain states:
  - taskResourceLocalHandlers: Overrides the resource of the specified Task states to run a local function.
  - waitTimeOverrides: Overrides the wait duration of the specified Wait states. The specifed override duration should be in milliseconds.

Example without options:

import { StateMachine } from 'aws-local-stepfunctions';

const machineDefinition = {
  StartAt: 'Hello World',
  States: {
    'Hello World': {
      Type: 'Task',
      Resource: 'arn:aws:lambda:us-east-1:123456789012:function:HelloWorld',
      End: true,
    },
  },
};

const stateMachine = new StateMachine(machineDefinition, { checkPaths: false });
const myInput = { value1: 'hello', value2: 123, value3: true };
const result = await stateMachine.run(myInput); // execute the state machine

console.log(result); // log the result of the execution

Example with options:

import { StateMachine } from 'aws-local-stepfunctions';

const machineDefinition = {
  StartAt: 'Hello World',
  States: {
    'Hello World': {
      Type: 'Task',
      Resource: 'arn:aws:lambda:us-east-1:123456789012:function:HelloWorld',
      Next: 'AddNumbers',
    },
    AddNumbers: {
      Type: 'Task',
      Resource: 'arn:aws:lambda:us-east-1:123456789012:function:AddNumbers',
      Next: 'Wait10Seconds',
    },
    Wait10Seconds: {
      Type: 'Wait',
      Seconds: 10,
      End: true,
    },
  },
};

function addNumbersLocal(input) {
  return input.num1 + input.num2;
}

const stateMachine = new StateMachine(machineDefinition, { checkPaths: false });
const myInput = { value1: 'hello', value2: 123, value3: true };
const result = await stateMachine.run(myInput, {
  overrides: {
    taskResourceLocalHandlers: {
      AddNumbers: addNumbersLocal, // call the `addNumbersLocal` function instead of invoking the Lambda function specified for the `AddNumbers` state
    },
    waitTimeOverrides: {
      Wait10Seconds: 500, // wait for 500 milliseconds instead of the 10 seconds specified in the `Wait10Seconds` state
    },
  },
});

console.log(result); // log the result of the execution

License

MIT