typescript 47 lines · 8 steps

Validating config with Zod schemas

A Zod schema validates untrusted config at runtime and produces a fully typed, guaranteed-valid object.

Explained by highlit

Zod Intermediate schema-validation runtime-safety type-inference error-reporting

1import { z } from "zod";
2 
3const DatabaseSchema = z.object({
4  host: z.string().min(1),
5  port: z.number().int().min(1).max(65535),
6  ssl: z.boolean().default(false),
7  pool: z.object({
8    min: z.number().int().nonnegative(),
9    max: z.number().int().positive(),
10  }).refine((p) => p.max >= p.min, {
11    message: "max must be >= min",
12    path: ["max"],
13  }),
14});
15 
16const ConfigSchema = z.object({
17  env: z.enum(["development", "staging", "production"]),
18  database: DatabaseSchema,
19  features: z.record(z.string(), z.boolean()).default({}),
20  workers: z.array(z.object({
21    name: z.string(),
22    concurrency: z.number().int().positive(),
23  })).min(1),
24});
25 
26export type Config = z.infer<typeof ConfigSchema>;
27 
28export interface ConfigIssue {
29  path: string;
30  message: string;
31}
32 
33export function loadConfig(raw: unknown): Config {
34  const result = ConfigSchema.safeParse(raw);
35  if (result.success) return result.data;
36 
37  const issues: ConfigIssue[] = result.error.issues.map((issue) => ({
38    path: issue.path.length ? issue.path.join(".") : "<root>",
39    message: issue.message,
40  }));
41 
42  const report = issues
43    .map((i) => `  \u2022 ${i.path}: ${i.message}`)
44    .join("\n");
45 
46  throw new Error(`Invalid configuration:\n${report}`);
47}

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STEP 01

Walkthrough

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Three takeaways

1Zod schemas double as both runtime validators and the single source of truth for static types.
2refine lets you attach cross-field invariants that simple field types can't express.
3safeParse plus issue mapping turns raw validation failures into readable, actionable error reports.

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