# schema-types [](https://www.npmjs.com/package/schema-types) [](https://github.com/schema-types/schema-types/actions) [](https://codecov.io/gh/schema-types/schema-types)
This library provides runtime and compile-type type schema definition and validation.
### Features
- Zero dependencies!
- High level of developer ergonomics
- Full modern TypeScript support
- IntelliSense support
## Installation
```shell
$ yarn add schema-types
```
## Example
```typescript
import * as T from 'schema-types'
// NOTE: documentation comments on the properties will appear in IntelliSense
const userType = T.object({
/** The user's name */
name: T.string(),
/** The user's age */
age: T.number(),
/** Is the user account locked? */
locked: T.optional(T.boolean()),
})
// Create a compile-time type alias for the schema type
type User = T.TypeOf
// Use the compile-time type
export const user: User = {
name: 'Alice',
age: 32,
}
// Unknown data from user input, an API response, etc
const data: unknown = ...
// Return any validation issues
T.validate(userType, data) //=> [] (no issues)
T.validate(userType, {name: 'Alice', age: '32'}) //=> [{type: 'INVALID_TYPE', message: 'Invalid type, expected number, got string 32', path: '/age'}]
// Use a type-guard to refine the type
if (T.is(userType, data)) {
// data is typed as `User`
}
// T.assert() throws an error if the data fails to validate
try {
T.assert(userType, data)
// data is typed as `User` (using TypeScript's `asserts` return type)
} catch (error) {
console.log(error.issues) // logs the issues causing validation failure
}
// Generate TypeScript code for codegen
T.code(userType) //=> {"name": string; "age": number; "locked"?: (boolean | undefined)}
```
## Type Compatibility
Types:
| TypeScript | schema-types |
| ------------------- | ------------------ |
| `any` | `T.any()` |
| `Array` | `T.array()` |
| `bigint` | `T.bigint()` |
| `boolean` | `T.boolean()` |
| `Function` | `T.function()` |
| `null` | `T.null()` |
| `number` | `T.number()` |
| `object` | `T.object()` |
| `Record` | `T.map()` |
| `string` | `T.string()` |
| `undefined` | `T.undefined()` |
| `unknown` | `T.unknown()` |
| `void` | `T.void()` |
| Literals | `T.literal()` |
| Literal Union | `T.literalUnion()` |
| Tuple | `T.tuple()` |
| Union | `T.union()` |
| Intersection | `T.intersection()` |
Modifiers:
| TypeScript | schema-types |
| ---------- | -------------- |
| Optional | `T.optional()` |
| Read-only | `T.readonly()` |
Not implemented:
| TypeScript | schema-types |
| ---------- | --------------- |
| Enums | Not Implemented |
| Generics | Not Implemented |
## Helpers
### `T.TypeOf`
Takes a type schema and infers the TypeScript type for that schema.
### `T.assert(schema, value)`
Checks to see if the value matches the supplied schema, and if not, throws an error.
### `T.is(schema, value)`
Returns a boolean indicating if the value matches the supplied schema.
### `T.validate(schema, value)`
Returns an array of validation issues, if any.
### `T.code(schema)`
Returns a string containing the TypeScript code representation of the schema, useful for code generation.
## Credits
This library was inspired by several other TypeScript runtime type libraries:
- [typebox](https://github.com/sinclairzx81/typebox)
- [io-ts](https://github.com/gcanti/io-ts)
- [zod](https://github.com/vriad/zod)
- [runtypes](https://github.com/pelotom/runtypes)
- [@punchcard/shape](https://github.com/punchcard/punchcard/tree/master/packages/%40punchcard/shape)
- [ajv](https://github.com/ajv-validator/ajv)
## License
MIT license, see `LICENSE`