const graph = new Graph();

graph.addNode(new Node('a', () => new Promise(...)));
graph.addNode(new Node('b', () => new Promise(...)));
graph.addNode(new Node('c', () => new Promise(...)));
graph.addNode(new Node('d', () => new Promise(...)));

graph.addDependency('b', 'a'); // b needs the data from a
graph.addDependency('d', 'c'); // d needs the data from c
graph.addDependency('c', 'a'); // c needs the data from a

graph.traverse().then(() => {
   // all nodes completed in order of dependence, in parallel when possible.
});

graph.getNode('a').awaitData().then((data)=> {
    console.log(data);
});
graph.getNode('b').awaitData().then((data)=> {
    console.log(data);
});
graph.getNode('c').awaitData().then((data)=> {
    console.log(data);
});
graph.getNode('d').awaitData().then((data)=> {
    console.log(data);
});