Microstruct

Less than 500B (gzipped) subset of Superstruct specialized in validating and typing data decoded from JSON.

Example

// ref: https://github.com/ianstormtaylor/superstruct#usage

import { is, object, number, string, array } from 'microstruct';

const Article = object({
  id: number(),
  title: string(),
  tags: array(string()),
  author: object({
    id: number(),
  }),
});

const data: unknown = {
  id: 34,
  title: 'Hello World',
  tags: ['news', 'features'],
  author: {
    id: 1,
  },
};

if (is(data, Article)) {
  // 'data' is guaranteed to be of type '{ id: number; title: string; tags:
  // string[]; author: { id: number } }' in this block.
}

Main Differences to Superstruct

No Support for `assert()`, `create()` or `validate()`

Of the core methods of Superstruct, only is() is supported.

No Support for Classes or Functions

Because Microstruct is specialized in validating and typing data decoded from JSON, structs validating classes and functions such as date and func are not supported.

However, you can still define them yourself.

const date = define<Date>(value =>
  value instanceof Date && !Number.isNaN(value.getTime()));

const data: unknown = new Date();

if (is(data, date)) {
  // 'data' is guaranteed to be of type 'Date' in this block.
}

`object` Accepts Extra Properties

object accepts extra properties like type.

const User = object({
  id: number(),
  name: string(),
});

const data = {
  id: 1,
  name: 'Jane Smith',
  email: 'jane@example.com',
};

if (is(data, User)) {
  // 'data' is guaranteed to be of type '{ id: number; name: string }' in this
  // block.
}

`record` Rejects `enums` and `literal` as Keys

record rejects enums and literal as keys, because they may produce wrong type annotations.

import { assert, enums, record, string } from 'superstruct';

const User = record(enums(['id', 'name']), string());

const data: unknown = { id: 'jsmith' };

assert(data, User);

// 'data.name' is typed as 'string', but actually 'undefined'.

Support for `parseJSON()`

parseJSON() returns a JavaScript value described by a JSON string, or undefined if parse or validation fails. It never throws an exception.

const json = '{"result":true, "count":42}';

const value = parseJSON(json, object({ result: boolean(), count: number() }));

if (value !== undefined) {
  // 'value' is guaranteed to be of type `{ result: boolean; count: number }` in
  // this block.
}

Getting Started

npm i microstruct

Note: To use Microstruct with TypeScript, typescript >=4.1.2 is required.

Author

iorate (Twitter)

License

Microstruct is licensed under MIT License.

microstruct

Package Exports

Readme