Guards

Guards protect operations before they run. Unlike middleware (which is observational), guards can block operations.

Define a Guard

const stopGuard = mesh.guard({ kind: "action", name: /^admin\./ }, ({ state }) => ({
  allow: state.user.role === "admin",
  reason: "Admin access is required."
}));

Guard Targets

Target	Description
{ kind: "action", name: "cart.*" }	Guard actions by name
{ kind: "transaction", name: /^checkout/ }	Guard transactions
{ kind: "mutation", name: "products.*" }	Guard mutations

The name field accepts exact strings, wildcards (*), or RegExp.

Guard Error

When a guard blocks an operation, StateMesh throws GuardError:

import { GuardError } from "statemesh-core";

try {
  adminAction();
} catch (error) {
  if (error instanceof GuardError) {
    console.log(error.metadata.reason);  // "Admin access is required."
  }
}

Remove a Guard

stopGuard(); // Stop guarding

Important Notes

TIP

Guards run before the operation starts. They prevent any state mutation or async work from beginning.

WARNING

Guards are evaluated synchronously. The guard function must return { allow, reason } — not a Promise.

Next Steps

• Plugins — Extend the mesh
• Middleware — Observational event listeners