JavaScript implementation of Graph Data Structure

graph.js

// Implement a Graph
// basic operations:
//  - add vertex (node)
//  - add edge (node -> node)

function GraphNode(val) {
  this.val = val;
  this.edges = {};
}

function Graph() {
  this.vertices = {};
}

// O(1) operation
Graph.prototype.addVertex = function(val) {
  // add vertex only if it does not exist.
  if (!this.vertices[val]) {
    this.vertices[val] = new GraphNode(val);
  }
};

// O(E) operation - edges
Graph.prototype.removeVertex = function(val) {
  if (this.vertices[val]) {
    // once you remove a vertex, you need to remove all edges pointing
    // to the vertex.
    delete this.vertices[val];
    
    Object.keys(this.vertices).forEach(function(key, index) {
      if (this.vertices[key].edges[val]) {
        delete this.vertices[key].edges[val];
      }
    }.bind(this));
  }
};

// O(1) operation
Graph.prototype.getVertex = function(val) {
  return this.vertices[val];
};

// O(1) operation
Graph.prototype.addEdge = function(start, end) {
  // check to see if vertices exists.
  // if it exists, set the edges and be done.
  if (this.vertices[start] && this.vertices[end]) {
    
    // check to see if edge exists, if it does, increment it's weight
    if (this.vertices[start].edges[end]) {
      this.vertices[start].edges[end].weight += 1;
    } else {
      
      // edge does not exist, set weight to 1.
      this.vertices[start].edges[end] = { weight: 1 };
    }
  }
};

// O(1) operation
Graph.prototype.removeEdge = function(start, end) {
  if (this.vertices[start] && this.vertices[end]) {
    if (this.vertices[start].edges[end]) {
      delete this.vertices[start].edges[end];
    }
  }
};

// O(1) operation
Graph.prototype.getEdge = function(start, end) {
  return this.vertices[start].edges[end] || null;
};


Graph.prototype.neighbors = function(val) {
  return this.vertices[val] ? this.vertices[val].edges : null;
};

var graph = new Graph();

graph.addVertex(5);
graph.addVertex(2);
graph.addVertex(6);
graph.addVertex(7);
graph.addEdge(2, 5);
graph.addEdge(6, 7);
graph.addEdge(7, 5);
console.log(graph.getEdge(2, 5));
console.log(graph.getEdge(6, 7));
graph.removeVertex(5);
console.log(graph.getEdge(2, 5));
console.log(graph.neighbors(6));
console.log(graph.neighbors(5));