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Formatting errors

Zod emphasizes completeness and correctness in its error reporting. In many cases, it's helpful to convert the $ZodError to a more useful format. Zod provides some utilities for this.

Consider this simple object schema.

const schema = z.object({
  username: z.string(),
  favoriteNumbers: z.array(z.number()),
});

Attempting to parse this invalid data results in an error containing two issues.

const result = schema.safeParse({
  username: 1234,
  favoriteNumbers: [1234, "4567"],
});
 
result.error!.issues;
[
  {
    expected: 'string',
    code: 'invalid_type',
    path: [ 'username' ],
    message: 'Invalid input: expected string, received number'
  },
  {
    expected: 'number',
    code: 'invalid_type',
    path: [ 'favoriteNumbers', 1 ],
    message: 'Invalid input: expected number, received string'
  },
  {
    code: 'unrecognized_keys',
    keys: [ 'extraKey' ],
    path: [],
    message: 'Unrecognized key: "extraKey"'
  }
];

z.treeifyError()

To convert ("treeify") this error into a nested object, use z.treeifyError().

const tree = z.treeifyError(result.error);
 
// =>
{
  errors: [ 'Unrecognized key: "extraKey"' ],
  properties: {
    username: { errors: [ 'Invalid input: expected string, received number' ] },
    favoriteNumbers: {
      errors: [],
      items: [
        undefined,
        {
          errors: [ 'Invalid input: expected number, received string' ]
        }
      ]
    }
  }
}

The result is a nested structure that mirrors the schema itself. You can easily access the errors that occured at a particular path. The errors field contains the error messages at a given path, and the special properties properties and items let you traverse deeper into the tree.

tree.properties?.username?.errors;
// => ["Invalid input: expected string, received number"]
 
tree.properties?.favoriteNumbers?.items?.[1]?.errors;
// => ["Invalid input: expected number, received string"];

Be sure to use optional chaining (?.) to avoid errors when accessing nested properties.

z.prettifyError()

The z.prettifyError() provides a human-readable string representation of the error.

const pretty = z.prettifyError(result.error);

This returns the following string:

✖ Unrecognized key: "extraKey"
✖ Invalid input: expected string, received number
  → at username
✖ Invalid input: expected number, received string
  → at favoriteNumbers[1]

z.formatError()

This has been deprecated in favor of z.treeifyError().

z.flattenError()

This has been deprecated in favor of z.treeifyError().

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