Using Zod to Parse a JSON String

I recently needed to parse a JSON string in TypeScript and validate the shape of the resulting data. I found a small utility from zod_utilz that handles both steps in one schema pipeline.

import { z } from "zod";

const stringToJSONSchema = z.string().transform((value, context) => {
  try {
    return JSON.parse(value);
  } catch {
    context.addIssue({ code: "custom", message: "Invalid JSON" });
    return z.NEVER;
  }
});

const MyDataSchema = z.object({
  foo: z.string(),
  bar: z.number(),
});

const jsonString = '{"foo": "hello", "bar": 42}';

const result = stringToJSONSchema.pipe(MyDataSchema).safeParse(jsonString);

The transform handles JSON syntax errors. Piping its output into MyDataSchema then validates the parsed value before the caller can use it.