trekhleb/javascript-algorithms · error · Error

Graph vertex must have a value

Error message

Graph vertex must have a value

What it means

GraphVertex's constructor requires a value (src/data-structures/graph/GraphVertex.js:8-10) because the value doubles as the vertex key - getKey() returns this.value verbatim - and every graph lookup depends on that key existing. Only undefined is rejected: null, 0, '' and false are all accepted as legitimate values.

Source

Thrown at src/data-structures/graph/GraphVertex.js:9

import LinkedList from '../linked-list/LinkedList';

export default class GraphVertex {
  /**
   * @param {*} value
   */
  constructor(value) {
    if (value === undefined) {
      throw new Error('Graph vertex must have a value');
    }

    /**
     * @param {GraphEdge} edgeA
     * @param {GraphEdge} edgeB
     */
    const edgeComparator = (edgeA, edgeB) => {
      if (edgeA.getKey() === edgeB.getKey()) {
        return 0;
      }

      return edgeA.getKey() < edgeB.getKey() ? -1 : 1;
    };

    // Normally you would store string value like vertex name.
    // But generally it may be any object as well
    this.value = value;
    this.edges = new LinkedList(edgeComparator);

View on GitHub (pinned to 85293e3e2b)

Solutions

1. Supply a concrete value or default: new GraphVertex(row.label ?? `vertex-${row.id}`) - only undefined throws, so null and falsy primitives are fine when intentional.
2. Validate records at the boundary and fail with your own clearer error before reaching the constructor.
3. If 'no value' is meaningful in your domain, pass null explicitly rather than leaving the argument out.

Example fix

// before
const vertex = new GraphVertex(row.label); // row.label === undefined -> Error

// after
const vertex = new GraphVertex(row.label ?? `vertex-${row.id}`);

// undefined is the ONLY rejected value - null, 0, '' and false are valid
const hasVertexValue = (value) => value !== undefined;

if (hasVertexValue(row.label)) {
  graph.addVertex(new GraphVertex(row.label));
} else {
  // record is malformed: report it before constructing
}

try {
  vertex = new GraphVertex(candidate);
} catch (error) {
  if (error.message === 'Graph vertex must have a value') {
    vertex = new GraphVertex(fallbackValue);
  } else {
    throw error;
  }
}

When it happens

Trigger: new GraphVertex() with no argument; new GraphVertex(obj.missingProperty) where parsing or destructuring produced undefined; new GraphVertex(row.name) where some records lack the field; a helper with an optional parameter that forwards undefined into the constructor.

Common situations: Building vertices from JSON/CSV rows where a column is missing or null-vs-absent varies between records; refactors that rename the field feeding the constructor; optional function parameters that silently propagate undefined.

Understand the failure class

Background: "missing required argument" and "the following required arguments were not provided": what required-argument errors mean and how to fix them — this error's family across 20 libraries.

Related errors

• Vertex has already been added before
• Edge has already been added before
• Edge not found in graph

AI-assisted analysis of trekhleb/javascript-algorithms@85293e3e2b (2026-08-24). Data as JSON: /api/errors/01c8893a27ae7ffb. Report an issue: GitHub.