Parsing and Transforming Data with Zod

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Overview

When I first started using Zod, I found that creating schemas, parsing data, and inferring types felt really natural. I wanted to write a few little snippets of how I have recently been using Zod to improve the data handling and type safety in a Typescript project.

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Creating a Zod Schema

import { z } from "zod"

export type MyData = z.infer<typeof myDataSchema>

export const myDataSchema = z.object({
  userId: z.string(),

  name: z.string(),

  signUpDate: z.coerce.datetime().optional(),

  greeting: z
    .string()
    .transform((userName) => `Hi, ${userName}`)
    .optional()
});

Most of this is straight forward Zod concepts, but what I thought was cool was the transform function.

I also like this pattern of inferring the type from Zod schema as you don't need to duplicate type information in an interface and a schema, but rather just use Zod to do all the work for you.

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Parsing a Zod Schema

Given the schema, this pattern will greatly simplify parsing the data into a typed object... something like this:

// data coming from a third-party integration
const someUnsafeData = {
  id: "12345",
  name: "Will Sather",
  date: "2024-04-19T04:07:22+0000",
};

// data being used in the application
const parsedData: MyData = myDataSchema.parse({
  userId: someUnsafeData.id,
  name: someUnsafeData.name,
  signUpDate: someUnsafeData.date,
  greeting: someUnsafeData.name,
});

As shown in the example, this is a useful way to create type safe data when integrating with third party APIs, but also, it can be helpful in other scenarios. The ones that come to mind when you have a lot of JSON data that needs to be typed, where a Date or a number might be stored as a string.

However, I found that Zod provides an even simpler API to handle that data casting called coerce. You'll see this on line 10 where Zod is smart enough to automatically convert and type check the input type.

Anyway, Zod documentation contains more information, use cases/examples, and helpful tips - worth checking out!