#104 @AssertType rejects a promise when used in async methods

README.md

@@ -257,6 +257,74 @@ new A().method(42) === 42; // true
 new A().method('42' as any); // will throw error
 ```
 
+### async and `Promise` returning methods 
+`AssertType` can also work correctly with `async` methods, returning promise rejected with `TypeGuardError`
+
+To enable this functionality, you need to emit decorators metadata for your TypeScript project.
+
+```json
+{
+    "compilerOptions": {
+      "emitDecoratorMetadata": true
+    }
+}
+```
+
+Then `AssertType` will work with async methods and `Promise` returning methods automatically.
+```typescript
+import { ValidateClass, AssertType } from 'typescript-is';
+
+@ValidateClass()
+class A {
+    async method(@AssertType({ async: true }) value: number) {
+        // You can safely use value as a number
+        return value;
+    }
+
+    methodPromise(@AssertType({ async: true }) value: number): Promise<number> {
+        // You can safely use value as a number
+        return Promise.resolve(value);
+    }
+}
+
+new A().method(42).then(value => value === 42 /* true */); 
+new A().method('42' as any).catch(error => {
+    // error will be of TypeGuardError type
+})
+new A().methodPromise('42' as any).catch(error => {
+    // error will be of TypeGuardError type
+})
+```
+
+If you want to throw synchronously for some reason, you can override the behaviour using with `@AssertType({ async: false })`:
+```typescript
+import { ValidateClass, AssertType } from 'typescript-is';
+
+@ValidateClass()
+class A {
+    async method(@AssertType({ async: false }) value: number) {
+        // You can safely use value as a number
+        return value;
+    }
+}
+
+new A().method(42).then(value => value === 42 /* true */);
+new A().method('42' as any); // will throw error
+```
+
+If you cannot or don't want to enable decorators metadata, you still make AssertType reject with promise using `@AssertType({ async: true })` 
+```typescript
+import { ValidateClass, AssertType } from 'typescript-is';
+
+@ValidateClass()
+class A {
+    async method(@AssertType({ async: true }) value: number) {
+        // You can safely use value as a number
+        return value;
+    }
+}
+```
+
 ## Strict equality (`equals`, `createEquals`, `assertEquals`, `createAssertEquals`)
 
 This family of functions check not only whether the passed object is assignable to the specified type, but also checks that the passed object does not contain any more than is necessary. In other words: the type is also "assignable" to the object. This functionality is equivalent to specifying `disallowSuperfluousObjectProperties` in the options, the difference is that this will apply only to the specific function call. For example:

index.d.ts

@@ -125,7 +125,7 @@ export function createAssertEquals<T>(): (object: any) => T;
    new A().method('0' as any); // will throw an error
    ```
  */
-export function AssertType(): (target: object, propertyKey: string | symbol, parameterIndex: number) => void;
+export function AssertType(options?: { async: boolean }): (target: object, propertyKey: string | symbol, parameterIndex: number) => void;
 
 /**
  * Overrides methods in the target class with a proxy that will first validate the argument types.

index.js

@@ -45,7 +45,11 @@ function AssertType(assertion, options = {}) {
     require('reflect-metadata');
     return function (target, propertyKey, parameterIndex) {
         const assertions = Reflect.getOwnMetadata(assertionsMetadataKey, target, propertyKey) || [];
-        assertions[parameterIndex] = { assertion, options };
+        if(Reflect.getOwnMetadata('design:returntype', target, propertyKey) === Promise) {
+            assertions[parameterIndex] = { assertion, options: Object.assign({ async: true }, options) };
+        } else {
+            assertions[parameterIndex] = { assertion, options };
+        }
         Reflect.defineMetadata(assertionsMetadataKey, assertions, target, propertyKey);
     };
 }
@@ -64,7 +68,12 @@ function ValidateClass(errorConstructor = TypeGuardError) {
                         }
                         const errorObject = assertions[i].assertion(args[i]);
                         if (errorObject !== null) {
-                            throw new errorConstructor(errorObject, args[i]);
+                            const errorInstance = new errorConstructor(errorObject, args[i]);
+                            if(assertions[i].options.async) {
+                                return Promise.reject(errorInstance);
+                            } else {
+                                throw errorInstance;
+                            }
                         }
                     }
                     return originalMethod.apply(this, args);

test-fixtures/issue-104.ts

@@ -0,0 +1,21 @@
+import {AssertType, ValidateClass} from '../index';
+
+@ValidateClass()
+export class AsyncMethods {
+    async asyncMethod(@AssertType() body: { test: string }): Promise<boolean> {
+        return true
+    }
+    async asyncMethodNoExplicitReturn(@AssertType() body: { test: string }) {
+        return true
+    }
+    promiseReturnMethod(@AssertType() body: { test: string }): Promise<boolean> {
+        return Promise.resolve(true)
+    }
+    async asyncOverride(@AssertType({ async: false }) body: { test: string }): Promise<boolean> {
+        return true
+    }
+    promiseOrOtherReturnMethod(@AssertType() body: { test: string }): Promise<boolean> | boolean{
+        return Promise.resolve(true)
+    }
+}
+

test/issue-104.ts

@@ -0,0 +1,25 @@
+import * as assert from 'assert';
+import {AsyncMethods} from '../test-fixtures/issue-104';
+
+describe('@ValidateClass(), @AssertType()', () => {
+    it('should return rejected promise for async methods', () => {
+        const instance = new AsyncMethods()
+        assert.rejects(instance.asyncMethod({invalid: 123} as any))
+    })
+    it('should return rejected promise for async methods with not explicit return type', () => {
+        const instance = new AsyncMethods()
+        assert.rejects(instance.asyncMethodNoExplicitReturn({invalid: 123} as any))
+    })
+    it('should return rejected promise for methods returning promise', () => {
+        const instance = new AsyncMethods()
+        assert.rejects(instance.promiseReturnMethod({invalid: 123} as any))
+    })
+    it('should throw synchronously if { async: false } option is set', () => {
+        const instance = new AsyncMethods()
+        assert.throws(() => instance.asyncOverride({invalid: 123} as any))
+    })
+    it('should throw synchronously method may return something other than promise', () => {
+        const instance = new AsyncMethods()
+        assert.throws(() => instance.promiseOrOtherReturnMethod({invalid: 123} as any))
+    })
+})

tsconfig-test.json

@@ -5,6 +5,7 @@
         "lib": [
             "es6"
         ],
+        "emitDecoratorMetadata": true,
         "experimentalDecorators": true,
         "noImplicitAny": true,
         "noUnusedLocals": true,
@@ -20,4 +21,4 @@
     "include": [
         "test"
     ]
-}
+}

tsconfig.json

@@ -5,6 +5,7 @@
         "lib": [
             "es6"
         ],
+        "emitDecoratorMetadata": true,
         "experimentalDecorators": true,
         "noImplicitAny": true,
         "noUnusedLocals": true,
@@ -17,4 +18,4 @@
     "include": [
         "src"
     ]
-}
+}