promi-safe

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promi-safe is a lightweight and type-safe promise wrapper that can validate the return value of a promise at runtime.

It easily integrates with various runtime type-checking libraries through the StandardSchema interface.

Motivation

When developing real-world applications, API responses may differ from the types expected by the frontend.

For example, required fields might be missing, or a value that should be a string may be returned as a number. Such discrepancies can trigger subtle bugs and make debugging challenging.

promi-safe validates the result of a promise according to a schema, helping to prevent these issues and enabling appropriate handling in case of validation failure.

Setup

npm install promi-safe
pnpm add promi-safe
pnpm add promi-safe

Usage

It is recommended to use this library together with libraries that satisfy the StandardSchema interface.
The example below uses zod.

import { makeSafePromise } from "promi-safe";
import { z } from "zod";

const promise = (await fetch("/test")).json();
const promiseWithSafe = makeSafePromise(apiCall);
const schema = z.object({ id: z.string() }); // with zod

const response = promiseWithSafe.safe(schema);

When abstracting an httpClient, it can be used even more conveniently.

import { type SafePromise, makeSafePromise } from "promi-safe";

export const createHttpClient = (): HttpClient => {
  return {
    get: <T>(url: string, options?: RequestOptions): SafePromise<T> =>
      makeSafePromise(request<T>("GET", url, undefined, options)),
    ...
  };
};

import { z } from "zod";

const schema = z.object({ id: z.string() }); // with zod
const response = await api.get("/test").safe(schema);

API

• validateResponse(promise)(schema, options?):
  Validates the provided promise's resolved value against the given schema. The options are as follows:

  • onFail: A callback function that is called with the issues when validation fails.
  • throwOnError: If true, a ValidationError is thrown when validation fails.

• makeSafePromise(promise):
  Extends the given promise by adding a safe method that enables the same validation as above.

• ValidationError
  An error class that is thrown when validation fails (when the throwOnError option is used). The error object includes an issues property containing the list of validation problems.

License

MIT