Preface

I said I want SIMPLE runtypes. Just functions that validate and return data. Combine them into complex types and TypeScript knows their structure. That's how runtypes work.

• Install
• Example
• Why?
• Benchmarks
• Documentation
  • Intro
  • Usage Examples
    • Strict Property Checks
    • Optional Properties
    • Nesting
    • Discriminating Unions
    • Custom Runtypes
  • Reference
  • Roadmap / Todos

Install

npm install simple-runtypes or yarn add simple-runtypes

Example

1. Define the Runtype:

import * as st from 'simple-runtypes'

const userRuntype = st.record({
    id: st.integer(),
    name: st.string(),
    email: st.optional(st.string()),
})

now, ReturnType<typeof userRuntype> is equivalent to

interface {
    id: number,
    name: string,
    email?: string
}

2. Use the runtype to validate untrusted data

userRuntype({id: 1, name: 'matt'})
// => {id: 1, name: 'matt'}

userRuntype({id: 1, name: 'matt', isAdmin: true})
// throws an st.RuntypeError: "invalid field 'isAdmin' in data"

Invoke a runtype with use to get a plain value back instead of throwing errors:

st.use(userRuntype, {id: 1, name: 'matt'})
// => {ok: true, result: {id: 1, name: 'matt'}}

st.use(userRuntype, {id: 1, name: 'matt', isAdmin: true})
// => {ok: false, error: FAIL}

st.getFormattedError(FAIL)
// => 'invalid keys in record: ["isAdmin"] at `<value>` in `{"id":1,"name": "matt", ... }`'

Not throwing errors is way more efficient and less obscure. Throwing errors and catching them outside is more convenient.

Why?

Why should I use this over the plethora of other runtype validation libraries available?

1. Strict: by default safe against proto injection attacks and unwanted properties
2. Fast: check the benchmark
3. Friendly: no use of eval, a small footprint and no dependencies
4. Flexible: optionally modify the data while it's being checked: trim strings, convert numbers, parse dates

Benchmarks

@moltar has done a great job comparing existing runtime type-checking libraries in moltar/typescript-runtime-type-benchmarks.

@pongo has benchmarked simple-runtypes against io-ts in pongo/benchmark-simple-runtypes.

Documentation

Intro

A Runtype is a function that:

1. receives an unknown value
2. returns that value or a copy if all validations pass
3. throws a RuntypeError when validation fails or returns ValidationResult when passed to use

interface Runtype<T> {
    (v: unknown) => T
}

Runtypes are constructed by calling factory functions. For instance, string creates and returns a string runtype. Check the factory functions documentation for more details.

Usage Examples

Strict Property Checks

When using record, any properties which are not defined in the runtype will cause the runtype to fail:

const strict = st.record({name: st.string()})

strict({name: 'foo', other: 123})
// => RuntypeError: Unknown attribute 'other'

To ignore single properties, use ignore, unknown or any:

const strict = st.record({name: st.string(), other: st.ignore()})

strict({name: 'foo', other: 123})
// => {name: foo, other: undefined}

Use sloppyRecord to only validate known properties and remove everything else:

const sloppy = st.sloppyRecord({name: st.string()})

sloppy({name: 'foo', other: 123, bar: []})
// => {name: foo}

Using any of record or sloppyRecord will keep you safe from any __proto__ injection or overriding attempts.

Optional Properties

Use the optional runtype to create optional properties:

const squareConfigRuntype = st.record({
  color: st.optional(st.string()),
  width?: st.optional(st.number()),
})

Nesting

Collection runtypes such as record, array, tuple take runtypes as their parameters:

const nestedRuntype = st.record({
  name: st.string(),
  items: st.array(st.record({ id: st.integer, label: st.string() })),
})

nestedRuntype({
  name: 'foo',
  items: [{ id: 3, label: 'bar' }],
}) // => returns the same data

Discriminating Unions

simple-runtypes supports Discriminating Unions via the union runtype.

The example found in the TypeScript Handbook translated to simple-runtypes:

const networkLoadingState = st.record({
  state: st.literal('loading'),
})

const networkFailedState = st.record({
  state: st.literal('failed'),
  code: st.number(),
})

const networkSuccessState = st.record({
  state: st.literal('success'),
  response: st.record({
    title: st.string(),
    duration: st.number(),
    summary: st.string(),
  })
})

const networdStateRuntype = st.union(
  networkLoadingState,
  networkFailedState,
  networkSuccessState,
)

type NetworkState = ReturnType<typeof networkStateRuntype>

Finding the runtype to validate a specific discriminating union with is done efficiently with a Map.

Custom Runtypes

Write your own runtypes as plain functions, e.g. if you want to turn a string into a BigInt:

const bigIntStringRuntype = st.string({match: /^-?[0-9]+n$/})

const bigIntRuntype = st.runtype((v) => {
    const stringCheck = st.use(bigIntStringRuntype, v)

    if (!stringCheck.ok) {
        return stringCheck.error
    }

    return BigInt(stringCheck.result.slice(0, -1))
})

bigIntRuntype("123n") // => 123n
bigIntRuntype("2.2") // => error: "expected string to match ..."

Reference

Basic runtypes that match JavaScript/TypeScript types:

• number
• string
• boolean
• null
• undefined
• enum
• literal

Meta runtypes:

• integer
• stringAsInteger
• ignore
• unknown
• any
• json

Objects and Array Runtypes:

• tuple
• array
• record
  • optional
• sloppyRecord
• dictionary

Combinators:

• union
• intersection
• omit
• pick
• partial
• TODO: get - similar to Type[key]

Shortcuts:

• nullOr
• undefinedOr

Roadmap / Todos

• size - a meta-runtype that imposes a size limit on types, maybe via convert-to-json and .length on the value passed to it
• rename stringLiteralUnion to literals or literalUnion and make it work on all types that literal accepts
• rename record to object: #69
• nonStrict modifier instead of sloppy: #68
• improve docs:
  • preface: what is a runtype and why is it useful
  • why: explain or link to example that shows "strict by default"
  • show that simple-runtypes is feature complete because it can
    1. express all TypeScript types
    2. is extendable with custom runtypes (add documentation)
  • add small frontend and backend example projects that show how to use simple-runtypes in production
• test all types with tsd
• add more combinators: partial, required, get, ...
• separate Runtype and InternalRuntype and type runtype internals (see this comment)