mermaid-js/mermaid · error · Error

Edges array is required in layout data

Error message

Edges array is required in layout data

What it means

Fifth and final guard in validateLayoutData: `data.edges` is present but not an array (an undefined edges field also triggers it, since Array.isArray(undefined) is false). The cose-bilkent layout needs an edges array — possibly empty — to compute edge routes. Thrown at layout.ts:73. Unlike nodes, this check doesn't accept missing edges; they must be an array.

Source

Thrown at packages/mermaid/src/rendering-util/layout-algorithms/cose-bilkent/layout.ts:73

export function validateLayoutData(data: LayoutData): boolean {
  if (!data) {
    throw new Error('Layout data is required');
  }

  if (!data.config) {
    throw new Error('Configuration is required in layout data');
  }

  if (!data.rootNode) {
    throw new Error('Root node is required');
  }

  if (!data.nodes || !Array.isArray(data.nodes)) {
    throw new Error('No nodes found in layout data');
  }

  if (!Array.isArray(data.edges)) {
    throw new Error('Edges array is required in layout data');
  }

  return true;
}

View on GitHub (pinned to d93e9c88c0)

Solutions

1. Always set data.edges to an array (use [] when there are no edges).
2. Confirm the diagram-db layer emits edges as an array key named `edges`.
3. If your data model uses a different key, map it to edges before layout.
4. Add Array.isArray(data.edges) validation upstream to fail with a clearer message.

Example fix

// before
{ config, rootNode, nodes, layoutAlgorithm: 'cose-bilkent' } // edges missing
// after
{ config, rootNode, nodes, edges: [], layoutAlgorithm: 'cose-bilkent' }

if (!Array.isArray(data?.edges)) throw new Error('LayoutData.edges must be an array');

function hasEdgesArray(d: any): d is { edges: unknown[] } { return Array.isArray(d?.edges); }

try { validateLayoutData(data); } catch (e) { if (/Edges array is required/.test(String(e))) { data.edges = []; validateLayoutData(data); } else throw e; }

When it happens

Trigger: A LayoutData with edges omitted entirely, or edges set to an object/Map/null. e.g. { config, rootNode, nodes, layoutAlgorithm } with no edges key. Array.isArray(null) is false, so explicitly-null edges also fail.

Common situations: A node-only diagram built manually without an edges field, a transform that stores edges under a different key (e.g. `connections`), or a fixture missing edges. Because the check requires an array, even 'no edges' must be expressed as [].

Related errors

• Root node is required
• No nodes found in layout data
• Layout data is required
• Configuration is required in layout data
• No nodes found in layout data

AI-assisted analysis of mermaid-js/mermaid@d93e9c88c0 (2026-08-12). Data as JSON: /api/errors/1e48116b4d827c9d. Report an issue: GitHub.