Graph.js

class Graph {
    constructor(){
        this.adjacentList = {};
        this.numberOfNodes = 0;
    }

    //for each vertex add an array that will hold adjacent vertex/vertices
    addVertex(node){
        this.adjacentList[node] = [];
        this.numberOfNodes++;
    }

    addEdge(node1, node2){
        //since undirected so we have to push bothways
        this.adjacentList[node1].push(node2);
        this.adjacentList[node2].push(node1);
    }

    //optional - displays the adjacency list thus formed
    displayCollections(){
        const allNodes = Object.keys(this.adjacentList);
        for(let node of allNodes){
            let nodeCollections = this.adjacentList[node];
            let connections = "";
            let vertex;

            for(vertex of nodeCollections){
                connections += vertex+ " ";
            }

            console.log(node + "-->"+connections);
        }
    }
}

const myGraph = new Graph();
myGraph.addVertex('0');
myGraph.addVertex('1');
myGraph.addVertex('2');
myGraph.addVertex('3');
myGraph.addVertex('4');
myGraph.addVertex('5');
myGraph.addVertex('6');

myGraph.addEdge('3','1');
myGraph.addEdge('3','4');
myGraph.addEdge('4','2');
myGraph.addEdge('4','5');
myGraph.addEdge('1','2');
myGraph.addEdge('1','0');
myGraph.addEdge('0','2');
myGraph.addEdge('6','5');

myGraph.displayCollections();