Grafn

Graph + Fn: Execute functions as a graph.

What it's for?

Grafn lets you execute sequences of async functions by defining them as vertices in a graph.

This allows you to easily define and manipulate complex dependencies in asynchronous code.

How can I use it?

In order to use it you must first create a graph.

const Grafn = require('grafn');

const graph = new Grafn();

Next you need to add some vertexes.

graph.vertex({
  name: 'root',
  action() {

    return 5;
  }
});

This is a vertex without dependencies, it means it can be executed without waiting for anything else. The return value of this function will be stored so it can be used by its dependents.

You can add dependencies by listing the names as an array in the vertex definition.

graph.vertex({
  name: 'addition',
  dependencies: ['root'],
  action(state) {

    return state.root + state.root;
  }
});

Notice how the result of the root vertex is available in this action.

Vertexes will be executed as soon as all of their dependencies are met. For example, consider the following graph

const Grafn = require('grafn');

const graph = new Grafn();

graph.vertex({
  name: 'root',
  action() {

    return 5;
  }
});

graph.vertex({
  name: 'addition',
  dependencies: ['root'],
  action(state) {

    return state.root + state.root;
  }
});

graph.vertex({
  name: 'subtraction',
  dependencies: ['root'],
  action(state) {

    return state.root - state.root;
  }
});

graph.vertex({
  name: 'multiplication',
  dependencies: ['root'],
  action(state) {

    return state.root * state.root;
  }
});

graph.vertex({
  name: 'division',
  dependencies: ['root'],
  action(state) {

    return state.root / state.root;
  }
});

graph.vertex({
  name: 'tally',
  dependencies: ['addition', 'subtraction', 'multiplication', 'division'],
  action(state) {

    console.log('+', state.addition);
    console.log('-', state.subtraction);
    console.log('*', state.multiplication);
    console.log('/', state.division);
  }
});

The addition, subtraction, multiplication, and division vertices will all run as soon as roott is executed. However, the final tally vertex won't run until all other operations are complete.

You can visualize the graph by using the graph.toString() method. This will output a graphviz digraph:

digraph {
    root
    addition
    root -> addition
    subtraction
    root -> subtraction
    multiplication
    root -> multiplication
    division
    root -> division
    tally
    addition -> tally
    subtraction -> tally
    multiplication -> tally
    division -> tally
}

You can easily change the shape of the graph by changing the dependencies array.

In order to start execution of the graph you should select which node to start from.

graph.run('root');

After an execution, you can use graph.toString() to check the result of an execution. It will highlight which nodes were executed successfully (green), and which nodes threw an error (red).

Acknowledgements

This project implements the same ideas behind fluorine, a similar graph based library. Grafn wouldn't exist without it.