Method add

src/graph.js:6–15

(x, y)

		}

		add (x, y) {
			let result = false;

			if (defined(this.nodes[x]) && defined(this.nodes[y])) {
				this.nodes[x].edges[y] = this.nodes[y].edges[x] = null;
				result = true;
			}

			return result;
		}

		adjacent (x, y) {
			const n = this.nodes[x];