Add nullable types to TypeScript typings

Author: LinusU

index.d.ts

@@ -1,32 +1,25 @@
-type AnySchema = NullSchema | BooleanSchema | NumberSchema | StringSchema | AnyEnumSchema | AnyArraySchema | AnyObjectSchema | AnyAllOptionalObjectSchema | AnyOneOfSchema
+type AnySchema = NullSchema | BooleanSchema | NullableBooleanSchema | NumberSchema | NullableNumberSchema | StringSchema | NullableStringSchema | AnyEnumSchema | AnyArraySchema | AnyNullableArraySchema | AnyObjectSchema | AnyNullableObjectSchema | AnyAllOptionalObjectSchema | AnyNullableAllOptionalObjectSchema | AnyOneOfSchema
 type StringKeys<T> = (keyof T) & string
 
-interface NullSchema {
-  type: 'null'
-}
+interface NullSchema { type: 'null' }
 
-interface BooleanSchema {
-  type: 'boolean'
-}
+interface BooleanSchema { type: 'boolean' }
+interface NullableBooleanSchema { type: ('boolean' | 'null')[] }
 
-interface NumberSchema {
-  type: 'number'
-}
+interface NumberSchema { type: 'number' }
+interface NullableNumberSchema { type: ('number' | 'null')[] }
 
-interface StringSchema {
-  type: 'string'
-}
+interface StringSchema { type: 'string' }
+interface NullableStringSchema { type: ('string' | 'null')[] }
 
 interface AnyEnumSchema extends EnumSchema<any> {}
-interface EnumSchema<Enum> {
-  enum: Enum[]
-}
+interface EnumSchema<Enum> { enum: Enum[] }
 
 interface AnyArraySchema extends ArraySchema<AnySchema> {}
-interface ArraySchema<ItemSchema extends AnySchema> {
-  type: 'array'
-  items: ItemSchema
-}
+interface ArraySchema<ItemSchema extends AnySchema> { type: 'array', items: ItemSchema }
+
+interface AnyNullableArraySchema extends NullableArraySchema<AnySchema> {}
+interface NullableArraySchema<ItemSchema extends AnySchema> { type: ('array' | 'null')[], items: ItemSchema }
 
 interface AnyObjectSchema extends ObjectSchema<Record<string, AnySchema>, string> {}
 interface ObjectSchema<Properties extends Record<string, AnySchema>, Required extends StringKeys<Properties>> {
@@ -36,13 +29,28 @@ interface ObjectSchema<Properties extends Record<string, AnySchema>, Required ex
   required: Required[]
 }
 
+interface AnyNullableObjectSchema extends NullableObjectSchema<Record<string, AnySchema>, string> {}
+interface NullableObjectSchema<Properties extends Record<string, AnySchema>, Required extends StringKeys<Properties>> {
+  additionalProperties?: boolean
+  type: ('object' | 'null')[]
+  properties: Properties
+  required: Required[]
+}
+
 interface AnyAllOptionalObjectSchema extends AllOptionalObjectSchema<Record<string, AnySchema>> {}
 interface AllOptionalObjectSchema<Properties extends Record<string, AnySchema>> {
   additionalProperties?: boolean
   type: 'object'
   properties: Properties
 }
 
+interface AnyNullableAllOptionalObjectSchema extends NullableAllOptionalObjectSchema<Record<string, AnySchema>> {}
+interface NullableAllOptionalObjectSchema<Properties extends Record<string, AnySchema>> {
+  additionalProperties?: boolean
+  type: ('object' | 'null')[]
+  properties: Properties
+}
+
 interface AnyOneOfSchema { oneOf: AnySchema[] }
 
 interface ArrayFromSchema<ItemSchema extends AnySchema> extends Array<TypeFromSchema<ItemSchema>> {}
@@ -55,11 +63,17 @@ type TypeFromSchema<Schema extends AnySchema> = (
     Schema extends EnumSchema<infer Enum> ? Enum
   : Schema extends NullSchema ? null
   : Schema extends BooleanSchema ? boolean
+  : Schema extends NullableBooleanSchema ? (boolean | null)
   : Schema extends NumberSchema ? number
+  : Schema extends NullableNumberSchema ? (number | null)
   : Schema extends StringSchema ? string
+  : Schema extends NullableStringSchema ? (string | null)
   : Schema extends ArraySchema<infer ItemSchema> ? ArrayFromSchema<ItemSchema>
+  : Schema extends NullableArraySchema<infer ItemSchema> ? (ArrayFromSchema<ItemSchema> | null)
   : Schema extends ObjectSchema<infer Properties, infer Required> ? ObjectFromSchema<Properties, Required>
+  : Schema extends NullableObjectSchema<infer Properties, infer Required> ? (ObjectFromSchema<Properties, Required> | null)
   : Schema extends AllOptionalObjectSchema<infer Properties> ? ObjectFromSchema<Properties, never>
+  : Schema extends NullableAllOptionalObjectSchema<infer Properties> ? (ObjectFromSchema<Properties, never> | null)
   : never
 )
 

test/typings.ts

@@ -343,3 +343,68 @@ if (overengineeredColorValidator(input)) {
   if (input !== 'yellow' && input !== 'cream' && input !== 'red' && input !== 'pink' && input !== 'green' && input !== 'olive' && input !== 'blue') assertType<'teal'>(input)
   if (input !== 'cream' && input !== 'red' && input !== 'pink' && input !== 'green' && input !== 'olive' && input !== 'blue' && input !== 'teal') assertType<'yellow'>(input)
 }
+
+const nullableStringValidator = createValidator({
+  type: ['string', 'null']
+})
+
+if (nullableStringValidator(input)) {
+  if (typeof input !== 'object') assertType<string>(input)
+  if (typeof input !== 'string') assertType<null>(input)
+}
+
+const nullableNameValidator = createValidator({
+  type: 'object',
+  properties: {
+    name: { type: ['string', 'null'] }
+  },
+  required: [
+    'name'
+  ]
+})
+
+if (nullableNameValidator(input)) {
+  if (typeof input.name !== 'object') assertType<string>(input.name)
+  if (typeof input.name !== 'string') assertType<null>(input.name)
+}
+
+const nullableInventoryValidator = createValidator({
+  type: 'object',
+  properties: {
+    inventory: {
+      type: ['array', 'null'],
+      items: { type: 'string' }
+    }
+  },
+  required: [
+    'inventory'
+  ]
+})
+
+if (nullableInventoryValidator(input)) {
+  if (input.inventory === null) assertType<null>(input.inventory)
+  if (input.inventory !== null) assertType<string[]>(input.inventory)
+}
+
+const nullableParentValidator = createValidator({
+  type: 'object',
+  properties: {
+    parent: {
+      type: ['object', 'null'],
+      properties: {
+        name: { type: 'string' }
+      },
+      required: [
+        'name' as 'name'
+      ]
+    }
+  },
+  required: [
+    'parent'
+  ]
+})
+
+if (nullableParentValidator(input)) {
+  if (input.parent === null) assertType<null>(input.parent)
+  if (input.parent !== null) assertType<string>(input.parent.name)
+}