.gitignore

node_modules/
*.js

A.ts

// Define a class for use later
export class A {

}

example1.ts

import { typed, override, addType } from './typed';
import { A } from './A';

addType({  // this is just an example of a defined type
  name: 'A',
  test: function (x: any) {
    return x instanceof A;
  }
});

@typed // need this here to actually attach the typed functions
class TypedFunctions {

  // some signitures work without any additional annotation
  @override('method')
  methodOne(x: string) {
    console.log('Received a string');
  }

  // theroetically all primitives and classes
  // note that the methoid name iteself doesn't matter
  @override('method')
  methodTwo_Number(x: number) {
    console.log('Received a number');
  }

  // abstract types do not work
  // you will need to duplicate the type in the decorator
  @override('method', ['A | Date'])  
  methodFour(x: A | Date) {
    console.log('Received an instance of A or a Date');
  }

  // The method you are overriding should have the most generic type signature
  // Note here we are overriding the method itself, otherwise it will not be part of the typed function
  // Because of how TS treats any, `any` types need to be explicit, otherwise the type is `Obejct` :(
  @override('method', ['any'])
  method(x: any) {
    console.log('Received something else');
  }
}

const typedFunctions = new TypedFunctions();

// now the `method` method is a typed-function
typedFunctions.method('Hello');
typedFunctions.method(123);
typedFunctions.method(new Date());

example2.ts

import { typed, override } from './typed';

@typed
class MathFunctions {
  // Add
  add(x: string, y: string): string;
  add(x: number, y: number): number;
  add(x: boolean, y: boolean): boolean;

  @override('add', ['number', 'number'])
  @override('add', ['string', 'string'])
  add(x: any, y: any): any {
    return x + y;
  }

  @override('add')
  or(x: boolean, y: boolean): boolean {
    return x || y;
  }

  // Subtract
  sub(x: boolean, y: boolean): boolean;
  sub(x: number, y: number): boolean;

  @override('sub', ['number', 'number'])
  sub(x: any, y: any): any {
    return x - y;
  }

  @override('sub')
  xor(x: boolean, y: boolean): boolean {
    return (x || y) && !(x && y);
  }

  // Multiply
  mul(x: string, y: number): string;
  mul(x: number, y: number): number;
  mul(x: boolean, y: boolean): boolean;

  @override('mul', ['number', 'number'])
  mul(x: any, y: any): any {
    return x * y;
  }

  @override('mul')
  private mulStrings(x: string, y: number): string {
    return x.repeat(y);
  }

  @override('mul')
  and(x: boolean, y: boolean): boolean {
    return x && y;
  }

  // Divide
  div(x: boolean, y: boolean): boolean;
  div(x: number, y: number): number;

  @override('div', ['number', 'number'])
  div(x: any, y: any): any {
    return x / y;
  }

  @override('div')
  nand(x: boolean, y: boolean): boolean {
    return !(x && y);
  }
}

const mathFns = MathFunctions.prototype;

console.log(mathFns.add(1, 2));
console.log(mathFns.add('A', 'B'));
console.log(mathFns.add(true, false));
// console.log(mathFns.add(true, '2'));
// console.log(mathFns.add('1', 2));

console.log(mathFns.sub(1, 2));
console.log(mathFns.sub(true, false));
// console.log(mathFns.sub('1', '2'));
// console.log(mathFns.sub(true, '2'));
// console.log(mathFns.sub('1', 2));

console.log(mathFns.mul(1, 2));
console.log(mathFns.mul('A', 2));
console.log(mathFns.mul(true, false));
// console.log(mathFns.mul(true, '2'));
// console.log(mathFns.mul('1', '2'));

console.log(mathFns.div(1, 2));
console.log(mathFns.div(true, false));
// console.log(mathFns.div('1', 2));
// console.log(mathFns.div(true, '2'));
// console.log(mathFns.div('1', '2'));

example3.ts

import autobind from 'autobind-decorator';
import { typed, override, addType } from './typed';

class Person {
  constructor(public firstname: string, public lastname: string) {

  }
}

addType({
  name: 'Person',
  test: function (x: any) {
    return x instanceof Person;
  }
});

@typed
class Hello {
  constructor(private world: string) {

  }

  hello(x?: Person | string) {
  }

  @override('hello')
  helloPerson(person: Person) {
    return(`Hello ${this.world} ${person.firstname} ${person.lastname}`);
  }

  @override('hello')
  helloWorld() {
    return(`Hello ${this.world}`);
  }

  @override('hello')
  helloName(name: string) {
    return(`Hello ${this.world} ${name}`);
  }
}

const hello = new Hello('Earthling');

console.log(hello.hello());
console.log(hello.hello.call({ world: 'Martian' }));
console.log(hello.hello('Mike'));
console.log(hello.hello(new Person('Mike', 'Dee')));

const helloFn = hello.hello;
console.log(helloFn.call({ world: 'Martian' }));
console.log(helloFn.apply({ world: 'Martian' }));
console.log(helloFn.bind({ world: 'Martian' })());

console.log(helloFn.call({ world: 'Venitian' }, 'Mike'));
console.log(helloFn.apply({ world: 'Venitian' }, ['Mike']));
console.log(helloFn.bind({ world: 'Venitian' })('Mike'));

index.d.ts

declare module 'typed-function' {
  export var create: any;
}

index.ts

/// <reference path="index.d.ts"/>

import './example1';
import './example2';
import './example3';

package-lock.json

{
  "name": "typescript-typed-test",
  "version": "1.0.0",
  "lockfileVersion": 1,
  "requires": true,
  "dependencies": {
    "autobind-decorator": {
      "version": "2.1.0",
      "resolved": "https://registry.npmjs.org/autobind-decorator/-/autobind-decorator-2.1.0.tgz",
      "integrity": "sha512-bgyxeRi1R2Q8kWpHsb1c+lXCulbIAHsyZRddaS+agAUX3hFUVZMociwvRgeZi1zWvfqEEjybSv4zxWvFV8ydQQ=="
    },
    "reflect-metadata": {
      "version": "0.1.10",
      "resolved": "https://registry.npmjs.org/reflect-metadata/-/reflect-metadata-0.1.10.tgz",
      "integrity": "sha1-tPg3BEFqytiZiMmxVjXUfgO5NEo="
    },
    "typed-function": {
      "version": "0.10.5",
      "resolved": "https://registry.npmjs.org/typed-function/-/typed-function-0.10.5.tgz",
      "integrity": "sha1-Lg8Yq9BlIZ+raUpEamXG0ZgYMsA="
    },
    "typescript": {
      "version": "2.6.1",
      "resolved": "https://registry.npmjs.org/typescript/-/typescript-2.6.1.tgz",
      "integrity": "sha1-7znN6ierrAtQAkLWcmq5DgyEZjE=",
      "dev": true
    }
  }
}

package.json

{
  "name": "typescript-typed-test",
  "version": "1.0.0",
  "description": "",
  "main": "index.js",
  "scripts": {
    "test": "echo \"Error: no test specified\" && exit 1"
  },
  "author": "",
  "license": "ISC",
  "devDependencies": {
    "typescript": "^2.6.1"
  },
  "dependencies": {
    "autobind-decorator": "^2.1.0",
    "reflect-metadata": "^0.1.10",
    "typed-function": "^0.10.5"
  }
}

tsconfig.json

{
  "compilerOptions": {
    /* Basic Options */                       
    "target": "es6",                          /* Specify ECMAScript target version: 'ES3' (default), 'ES5', 'ES2015', 'ES2016', 'ES2017', or 'ESNEXT'. */
    "module": "commonjs",                     /* Specify module code generation: 'commonjs', 'amd', 'system', 'umd' or 'es2015'. */
    // "lib": [],                             /* Specify library files to be included in the compilation:  */
    // "allowJs": true,                       /* Allow javascript files to be compiled. */
    // "checkJs": true,                       /* Report errors in .js files. */
    // "jsx": "preserve",                     /* Specify JSX code generation: 'preserve', 'react-native', or 'react'. */
    // "declaration": true,                   /* Generates corresponding '.d.ts' file. */
    // "sourceMap": true,                     /* Generates corresponding '.map' file. */
    // "outFile": "./",                       /* Concatenate and emit output to single file. */
    // "outDir": "./",                        /* Redirect output structure to the directory. */
    // "rootDir": "./",                       /* Specify the root directory of input files. Use to control the output directory structure with --outDir. */
    // "removeComments": true,                /* Do not emit comments to output. */
    // "noEmit": true,                        /* Do not emit outputs. */
    // "importHelpers": true,                 /* Import emit helpers from 'tslib'. */
    // "downlevelIteration": true,            /* Provide full support for iterables in 'for-of', spread, and destructuring when targeting 'ES5' or 'ES3'. */
    // "isolatedModules": true,               /* Transpile each file as a separate module (similar to 'ts.transpileModule'). */
                                              
    /* Strict Type-Checking Options */        
    "strict": true,                           /* Enable all strict type-checking options. */
    // "noImplicitAny": true,                 /* Raise error on expressions and declarations with an implied 'any' type. */
    // "strictNullChecks": true,              /* Enable strict null checks. */
    // "noImplicitThis": true,                /* Raise error on 'this' expressions with an implied 'any' type. */
    // "alwaysStrict": true,                  /* Parse in strict mode and emit "use strict" for each source file. */
                                              
    /* Additional Checks */                   
    // "noUnusedLocals": true,                /* Report errors on unused locals. */
    // "noUnusedParameters": true,            /* Report errors on unused parameters. */
    // "noImplicitReturns": true,             /* Report error when not all code paths in function return a value. */
    // "noFallthroughCasesInSwitch": true,    /* Report errors for fallthrough cases in switch statement. */
                                              
    /* Module Resolution Options */           
    // "moduleResolution": "node",            /* Specify module resolution strategy: 'node' (Node.js) or 'classic' (TypeScript pre-1.6). */
    // "baseUrl": "./",                       /* Base directory to resolve non-absolute module names. */
    // "paths": {},                           /* A series of entries which re-map imports to lookup locations relative to the 'baseUrl'. */
    // "rootDirs": [],                        /* List of root folders whose combined content represents the structure of the project at runtime. */
    // "typeRoots": [],                       /* List of folders to include type definitions from. */
    // "types": [],                           /* Type declaration files to be included in compilation. */
    // "allowSyntheticDefaultImports": true,  /* Allow default imports from modules with no default export. This does not affect code emit, just typechecking. */
                                              
    /* Source Map Options */                  
    // "sourceRoot": "./",                    /* Specify the location where debugger should locate TypeScript files instead of source locations. */
    // "mapRoot": "./",                       /* Specify the location where debugger should locate map files instead of generated locations. */
    // "inlineSourceMap": true,               /* Emit a single file with source maps instead of having a separate file. */
    // "inlineSources": true,                 /* Emit the source alongside the sourcemaps within a single file; requires '--inlineSourceMap' or '--sourceMap' to be set. */
                                              
    /* Experimental Options */                
    "experimentalDecorators": true,        /* Enables experimental support for ES7 decorators. */
    "emitDecoratorMetadata": true          /* Enables experimental support for emitting type metadata for decorators. */
  }
}

typed.ts

/// <reference path="index.d.ts"/>

import 'reflect-metadata';
import * as Typed from 'typed-function';

export const typedApi = Typed.create();

export const addType = typedApi.addType.bind(typedApi);

// decorator methods
export function typed<T extends { new (...args: any[]): {} }>(constructor: T) {
  const target = constructor.prototype;

  if (Reflect.hasMetadata('design:signatures', target)) {
    const signatures = Reflect.getMetadata('design:signatures', target) || {};

    // for each method
    for (const key in signatures) {
      const getMethod = typedApi(key, signatures[key]);
      const fn = function(this: any, ...args: any[]) {
        return getMethod(...args).apply(this, args);
      };

      target[key] = function(...args: any[]) {
        return getMethod(...args).apply(this, args);
      };
    }
  }
  return constructor;
}

export function override(name: string, paramtypes?: string[]) {
  return function override<T>(
    target: any,
    propertyKey: string,
    descriptor: TypedPropertyDescriptor<T>
  ) {
    if (typeof Reflect === 'object') {
      paramtypes =
        <string[]>paramtypes ||
        Reflect.getMetadata('design:paramtypes', target, propertyKey);
      const typesKey = paramtypes.map(normalizeName).join(',');

      const method = target[propertyKey];

      if (typeof method === 'function') {
        const signatures =
          Reflect.getMetadata('design:signatures', target) || {};
        signatures[name] = signatures[name] || {};
        signatures[name][typesKey] = () => method;

        Reflect.defineMetadata('design:signatures', signatures, target);
      }
    }
  };

  function normalizeName(x: any) {
    x = typeof x === 'string' ? x : x.name;
    if (x === 'String') {
      return 'string';
    }
    if (x === 'Number') {
      return 'number';
    }
    if (x === 'Boolean') {
      return 'boolean';
    }
    return x;
  }
}