How can I reference class instances that I have passed into a Map as keys JavaScript

问题

I am implementing a graph class using a Map as an adjacency list, with a simple class Vertex that I am using to represent each node in the graph:

export class Vertex {
    constructor(value) {
        if (value) this.value = value;
        else throw new Error("Value must be specified");
    }

    getValue() {
        return this.value;
    }

    setValue(value) {
        if (value) this.value = value;
        else throw new Error("Value must be specified");
    }
}

Then in my graph class I have implemented a constructor and 2 methods for adding vertices and edges:

export class UndirectedGraph {
    constructor() {
        this.adjacencyList = new Map();
    }

    addVertex(value) {
        if (value) {
            const vertex = new Vertex(value);
            this.adjacencyList.set(vertex, []);
        }
    }

    addEdge(to, from) {
        if (
            !to ||
            !from ||
            !(to.constructor === Vertex && from.constructor === Vertex)
        ) {
            throw new Error("Arguments must be of type Vertex");
        }
        if (
            !this.adjacencyList.get(to) ||
            !this.adjacencyList.get(from)
        ) {
            throw new Error(
                "Both arguments must already be nodes in this undirected graph"
            );
        }
        this.adjacencyList.get(to).push(from);
        this.adjacencyList.get(from).push(to);
    }

    getAdjacencyList() {
        return this.adjacencyList;
    }
}

Then I want to call the addEdge() function to create an edge between 2 instances of type Vertex:

const graph = new UndirectedGraph();
graph.addVertex("A");
graph.addVertex("B");
graph.addVertex("B");
graph.addEdge(..., ...);

What do I pass to the addEdge() function to create an edge between "A" and a particular instance of "B"? I have no variable for the Vertex instances that I can reference.

I want the graph to be able to store duplicate values, such as names, so using class instances seems like the obvious choice but now I am stuck on how to access the values they contain because I am unsure how to search for class instances within the Map i.e. graph.getAdjacencyList().get(...). All help appreciated

回答1:

Given your addVertex method creates the Vertex instance and the addEdge method expects that very instance as a parameter, you need to make it available to the caller of these methods - by returning it:

…
addVertex(value) {
    if (value) {
        const vertex = new Vertex(value);
        this.adjacencyList.set(vertex, []);
        return vertex;
    }
    // else throw new Error("no value given")?
}
…

Then you can use it like

const graph = new UndirectedGraph();
const vertex1 = graph.addVertex("A");
const vertex2 = graph.addVertex("B");
const vertex3 = graph.addVertex("B");
graph.addEdge(vertex1, vertex2);
graph.addEdge(vertex1, vertex3);
graph.addEdge(vertex2, vertex3);

来源：https://stackoverflow.com/questions/59309381/how-can-i-reference-class-instances-that-i-have-passed-into-a-map-as-keys-javasc

标签

javascript

class

graph

vertex