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));

Hey Terence,

Thank you for showing how to implement the graph data structure in JavaScript. I'm new to data structures and your code helped guide me in the right direction.

However, I have a question:

Could lines 30 to 34 be simplified slightly by the following?

Object.values(this.vertices).forEach((vertex) => { if (vertex.connectedTo[value]) { delete vertex.connectedTo[value]; } }.bind(this));