the data structure for a directed graph

Digraph.js

export class Digraph { // exported so we can use it in topological sort
  constructor(v) {
    this.v = v; // initialize the number of vertices
    this.e = 0; // and edges
    this.adj = {}; // this object contains thevertices connected to each vertex.
  }

  addEdge(v, w) {
    if (!adj[v]) adj[v] = []; // check if the vertex already exist, if not, created it
    adj[v].push(w); // push the connecting edge vertex to its array of vertices
    e++; // increment the number of edges
  }
  adj(v) { return adj[v]; } // return all the vertices connected to v

  V() { return v; } // return number of vertices

  E() { return e; } // return number of edges

  /**
   * Reverses the graph direction
   * For directed graphs only
   * @param g
   * @return reversed graph
   */
  reverse() {
    Digraph rev = new Digraph(v);
    // for each of the vertices, get the other vertices connected to it and addEdge in     // reverse order
    for (let i = 0; i < v; i++) {
      for (let v of adj(i)) {
        rev.addEdge(v, i);
      }
    }
    return rev;
  }
  run() {
    Digraph test = new Digraph(4);
    test.addEdge(0, 1);
    test.addEdge(1, 2);
    test.addEdge(1, 3);
    test.addEdge(3, 0);
    console.log(test.E() + " edges");  // 4
    console.log(test.V() + " vertices"); // 4
    for (let v of test.adj(1)) {
      console.log("1->" + v); // 2 3
    }
    Digraph revTest = test.reverse();
    for (let v of revTest.adj(1)) {
      console.log("1->" + v); // 0
    }
  }
}