Graph implementation

Graph.js

var Graph = function() {
  this.verticesMap = new Map();
  this.edgesCount = 0;
};

Graph.prototype.getNumVertices = function() {
  return this.verticesMap.size;
}

Graph.prototype.getNumEdges = function() {
  return this.edgesCount;
}

Graph.prototype.validateVertex = function(v) {
  if (!this.hasVertex(v)) {
    throw new Error("Illegal Vertex :" + v + " is not a vertex");
  }
}

Graph.prototype.degree = function(v) {
  this.validateVertex(v);
  return this.verticesMap.get(v).length;
}

Graph.prototype.addEdge = function(v, w) {
  if (!this.hasVertex(v)) this.addVertex(v);
  if (!this.hasVertex(w)) this.addVertex(w);
  if (!this.hasEdge(v, w)) this.edgesCount++;
  this.verticesMap.get(v).add(w);
  this.verticesMap.get(w).add(v);
}

Graph.prototype.addVertex = function(v) {
  if (!this.hasVertex(v)) this.verticesMap.set(v, new Set());
}

Graph.prototype.hasEdge = function(v, w) {
  this.validateVertex(v);
  this.validateVertex(w);
  return this.verticesMap.get(v).has(w);
}

Graph.prototype.hasVertex = function(v) {
  return this.verticesMap.has(v);
}

Graph.prototype.toString = function() {
  string = "";

  for (var v in this.verticesMap.keys()) {
    string += v.toString() + ": ";
    for (let w of this.verticesMap.get(v).values()) {
      string += w.toString() + " ";
    }
    string += "\n";
  }

  return string;
}

var graph = new Graph();

graph.addEdge("A", "B");
graph.addEdge("A", "C");
graph.addEdge("C", "D");
graph.addEdge("D", "E");
graph.addEdge("D", "G");
graph.addEdge("E", "G");
graph.addVertex("H");

console.log(graph);

console.log("Vertices: " + graph.getNumVertices());
console.log("Edges: " + graph.getNumEdges());