gen-typed-validators

Automatically generate runtime validators from your Flow or TypeScript type definitions! (using typed-validators)

How it works
Type Walking
Limitations
CLI

How it works

Say you want to generate validators for a User type. Just add a const UserType: t.TypeAlias<User> = null declaration after it and run this codemod:

// User.ts

export type Address = {
  line1: string
  line2?: string
  city: string
  zipCode: string
}

export type User = {
  email: string
  firstName?: string
  lastName?: string
  address?: Address
}

export const UserType: t.TypeAlias<User> = null

$ gen-typed-validators User.ts

/Users/andy/github/typed-validators-codemods/User.ts
======================================

+ modified - original

@@ -1,15 +1,44 @@
+import * as t from 'typed-validators'
 export type Address = {
   line1: string
   line2?: string
   city: string
   zipCode: string
 }

+export const AddressType: t.TypeAlias<Address> = t.alias(
+  'Address',
+  t.object({
+    required: {
+      line1: t.string(),
+      city: t.string(),
+      zipCode: t.string(),
+    },
+
+    optional: {
+      line2: t.string(),
+    },
+  })
+)
+
 export type User = {
   email: string
   firstName?: string
   lastName?: string
   address?: Address
 }

-export const UserType: t.TypeAlias<User> = null
+export const UserType: t.TypeAlias<User> = t.alias(
+  'User',
+  t.object({
+    required: {
+      email: t.string(),
+    },
+
+    optional: {
+      firstName: t.string(),
+      lastName: t.string(),
+      address: t.ref(() => AddressType),
+    },
+  })
+)

? write: (y/N)

Type Walking

Notice that the above example also creates an AddressType validator for the Address type, since Address is used in the User type. gen-typed-validators will walk all the dependent types, even if they're imported. For example:

// Address.ts

export type Address = {
  line1: string
  line2?: string
  city: string
  zipCode: string
}

// User.ts

import { Address } from './Address'

export type User = {
  email: string
  firstName?: string
  lastName?: string
  address?: Address
}

export const UserType: t.TypeAlias<User> = null

$ gen-typed-validators User.ts

/Users/andy/github/typed-validators-codemods/Address.ts
======================================

+ modified - original

@@ -1,6 +1,22 @@
+import * as t from 'typed-validators'
 export type Address = {
   line1: string
   line2?: string
   city: string
   zipCode: string
 }
+
+export const AddressType: t.TypeAlias<Address> = t.alias(
+  'Address',
+  t.object({
+    required: {
+      line1: t.string(),
+      city: t.string(),
+      zipCode: t.string(),
+    },
+
+    optional: {
+      line2: t.string(),
+    },
+  })
+)



/Users/andy/github/typed-validators-codemods/User.ts
======================================

+ modified - original

@@ -1,10 +1,25 @@
-import { Address } from './Address'
+import { Address, AddressType } from './Address'

+import * as t from 'typed-validators'
+
 export type User = {
   email: string
   firstName?: string
   lastName?: string
   address?: Address
 }

-export const UserType: t.TypeAlias<User> = null
+export const UserType: t.TypeAlias<User> = t.alias(
+  'User',
+  t.object({
+    required: {
+      email: t.string(),
+    },
+
+    optional: {
+      firstName: t.string(),
+      lastName: t.string(),
+      address: t.ref(() => AddressType),
+    },
+  })
+)

? write: (y/N)

Limitations

This codemod currently doesn't preserve formatting, though if it finds prettier installed in your project, it will format the generated code using prettier.
Definitely not all types are supported. The goal will always be to support a subset of types that can be reliably validated at runtime.

Supported types:
- All primitive values
- any
- unknown/mixed
- Arrays
- Tuples
- Unions (|)
- Intersections (&)
- Objects or interfaces without indexers or methods
  - Flow exception: only a single indexer, to indicate a record type ({ [string]: number })
  - TS execption: indexers to allow additional properties
    - { foo: number, [string]: any }
    - { foo: number, [string]: unknown }
    - { foo: number, [string | symbol]: any }
    - { foo: number, [string | symbol]: unknown }
    - { foo: number, [any]: any }
    - { foo: number, [any]: unknown }
- TS Record types
- Interface extends
- Flow exact and inexact object types
- Flow object type spread {| foo: number, ...Bar |}, { foo: number, ...$Exact<Bar>, ... }
- Class instance types
- Type aliases
- Readonly types are converted as-is (but not enforced at runtime, since readonly is strictly a compile-time hint):
  - TS readonly
  - Flow $ReadOnly
  - Flow $ReadOnlyArray
Right now the generated validator name is ${typeName}Type and this isn't customizable. In the future I could change it to infer from the starting validator declaration(s).
Imports from node_modules aren't currently supported. It may be possible in the future when a package already contains generated validators, and it can find them along with the types in .d.ts or .js.flow files.

CLI

gen-typed-validators <files>

Options:
      --version  Show version number                                   [boolean]
  -q, --quiet    reduce output                                         [boolean]
  -w, --write    write without asking for confirmation                 [boolean]
  -c, --check    check that all validators match types                 [boolean]
      --help     Show help                                             [boolean]

Without the -w or -c option, it will print a diff for any changes it would make, and ask if you want to write the changes.