Simple undirected graph implementation in JavaScript

undirected-graph.js

var Graph = function() {
  this.nodes = {};
  this.edges = {};
};

Graph.prototype.addNode = function(node) {
  this.nodes[node] = node;
};

Graph.prototype.contains = function(node) {
  return this.nodes[node] ? true : false;
};

Graph.prototype.removeNode = function(node) {
  if (this.contains(node)) {
    delete this.nodes[node];
  }
};

Graph.prototype.hasEdge = function(fromNode, toNode) {
  for (var key in this.edges) {
    var searchOne = this.edges[key][0] === fromNode && this.edges[key][1] === toNode;
    var searchTwo = this.edges[key][1] === fromNode && this.edges[key][0] === toNode;
    if (searchOne || searchTwo) return true;
  }
  return false;
};

Graph.prototype.addEdge = function(fromNode, toNode) {
  this.edges[fromNode] = [fromNode, toNode];
};

Graph.prototype.removeEdge = function(fromNode, toNode) {
  if (this.hasEdge(fromNode, toNode)) {
    delete this.edges[fromNode];
  }
};

Graph.prototype.forEachNode = function(callback) {
  for (var node in this.nodes) {
    callback(node);
  }
};