Recursively convert ZodError to a string, or array of issue descriptions.

zodErrorToString.ts

import { type ZodError, type ZodIssue } from "zod";

export function zodErrorToString(error: ZodError, separator = ", ") {
  return zodIssuesToStrings(error.issues).join(separator);
}

function zodIssuesToStrings(obj: ZodIssue[]) {
  let results: string[] = [];

  function traverse(node: ZodIssue | ZodIssue[]) {
    if (!Array.isArray(node)) {
      if (node.path && Array.isArray(node.path) && node.message) {
        results.push(
          `${node.path.length ? node.path.join(".") + ": " : ""}${
            node.message
          }`,
        );
      }
    }

    // Recursively traverse through arrays and objects to cover for issues in z.union() et. al.
    for (let key in node) {
      if (
        typeof (node as never as Record<string, unknown>)[key] === "object" &&
        (node as never as Record<string, unknown>)[key] !== null
      ) {
        traverse(node[key as never]);
      }
    }
  }

  // Start traversing from the root object
  traverse(obj);

  return results;
}

Usage:

const zodSchema = z.object({ ... });
const data = { ... };

try {
  const result = zodSchema.parse(data);
} catch (error) {
  if (error instanceof ZodError) {
    console.error("Validation error: ", zodErrorToString(error));
  }
}