Zod CoerceArray

coerceArray Function

When using Zod for schema validation, you sometimes face the challenge where your API should accept both single values and arrays. The coerceArray function elegantly solves this problem by reliably transforming any input into an array format. No more manual Array.isArray() checking! 🎉

import type { ZodType } from 'zod';
import { z } from 'zod';

export function coerceArray<T extends ZodType>(schema: T) {
  return z
    .union([schema, z.array(schema)])
    .transform((rel) => (Array.isArray(rel) ? rel : [rel]) as T['_output'][]);
}

Usage Example

The following example shows how coerceArray works in practice. Whether it's a single value or already an array, the result is always consistent:

import { z } from 'zod';
import { coerceArray } from './coerceArray';

const schema = coerceArray(z.enum(['active', 'inactive']));

// Validating single values
schema.parse('active'); // ['active']
schema.parse(['active', 'inactive']); // ['active', 'inactive']