refactor: improve typings (#45)

* Add type guard, generic, and test

* Improve generic naming

* Add ErrorFSA alias

* Write test correctly to avoid confusion

* Add `someField` validation

* Add somefield test

* Add semi-colon, move tsc to posttest

* Add 3 more semi-colon

* Remove optional designation.

Since `payload` and `meta` is generic, user can specify `void` or `undefined` to indicate it does not present.

Removing the optional designation improves type guard.

see `isCustomAction4()` for example

* Fix more linting issue

* Adding eslint for typescript. Update yarn.lock

* Change typescript-eslint-parser to devDeps

* Move eslint-plugin-typescirpt to devDeps also.

.eslintrc.js

@@ -7,6 +7,10 @@ module.exports = {
   "globals": {
     "expect": true
   },
+  "parser": "typescript-eslint-parser",
+  "plugins": [
+    "typescript"
+  ],
   "rules": {
     "no-use-before-define": ["error", "nofunc"],
     "no-unused-expressions": 0,

package.json

@@ -14,7 +14,8 @@
     "lint": "eslint src/ test/",
     "prepublish": "npm test && npm run build",
     "pretest": "npm run lint",
-    "test": "cross-env NODE_ENV=test nyc mocha"
+    "test": "cross-env NODE_ENV=test nyc mocha",
+    "posttest": "tsc"
   },
   "repository": {
     "type": "git",
@@ -41,9 +42,12 @@
     "eslint": "^3.10.2",
     "eslint-config-airbnb-base": "^11.0.1",
     "eslint-plugin-import": "^2.2.0",
+    "eslint-plugin-typescript": "^0.1.0",
     "mocha": "^3.1.2",
     "nyc": "^10.0.0",
-    "rimraf": "^2.5.4"
+    "rimraf": "^2.5.4",
+    "typescript": "^2.0.10",
+    "typescript-eslint-parser": "^1.0.2"
   },
   "dependencies": {
     "lodash.isplainobject": "^4.0.6",

src/index.d.ts

@@ -1,4 +1,4 @@
-export interface FluxStandardAction {
+export interface FluxStandardAction<Payload, Meta> {
   /**
    * The `type` of an action identifies to the consumer the nature of the action that has occurred.
    * Two actions with the same `type` MUST be strictly equivalent (using `===`)
@@ -11,7 +11,7 @@ export interface FluxStandardAction {
    * By convention, if `error` is `true`, the `payload` SHOULD be an error object.
    * This is akin to rejecting a promise with an error object.
    */
-  payload?: any;
+  payload: Payload;
   /**
    * The optional `error` property MAY be set to true if the action represents an error.
    * An action whose `error` is true is analogous to a rejected Promise.
@@ -23,20 +23,29 @@ export interface FluxStandardAction {
    * The optional `meta` property MAY be any type of value.
    * It is intended for any extra information that is not part of the payload.
    */
-  meta?: any
+  meta: Meta;
 }
 
+export interface ErrorFluxStandardAction<CustomError extends Error, Meta> extends FluxStandardAction<CustomError, Meta> {
+  error: true;
+}
+
+/**
+ * Alias for FluxStandardAction.
+ */
+export type FSA<Payload, Meta> = FluxStandardAction<Payload, Meta>;
+
 /**
- * Alias to FluxStandardAction for shorthand
+ * Alias for ErrorFluxStandardAction.
  */
-export type FSA = FluxStandardAction;
+export type ErrorFSA<CustomError extends Error, Meta> = ErrorFluxStandardAction<CustomError, Meta>;
 
 /**
  * Returns `true` if `action` is FSA compliant.
  */
-export function isFSA(action: any): boolean;
+export function isFSA<Payload, Meta>(action: any): action is FluxStandardAction<Payload, Meta>;
 
 /**
  * Returns `true` if `action` is FSA compliant error.
  */
-export function isError(action: any): boolean;
+export function isError<CustomError extends Error, Meta>(action: any): action is ErrorFluxStandardAction<CustomError, Meta>;

test/typings-test.ts

@@ -0,0 +1,78 @@
+import { FluxStandardAction, isError, isFSA } from '../src';
+
+interface CustomPayload {
+  a: number;
+}
+
+interface CustomMetadata {
+  b: string;
+}
+
+interface MyError extends Error {
+  someField: string;
+}
+
+function createCustomAction(payload: CustomPayload) {
+  return {
+    type: 'custom',
+    payload
+  };
+}
+
+function isCustomAction(action: FluxStandardAction<any, any>): action is FluxStandardAction<CustomPayload, any> {
+  return isFSA(action) && action.type === 'custom';
+}
+
+function isCustomAction2(action: FluxStandardAction<any, any>): action is FluxStandardAction<CustomPayload, CustomMetadata> {
+  return isFSA(action) && action.type === 'custom2';
+}
+
+function isCustomAction3(action: any): action is FluxStandardAction<void, string> {
+  return isFSA(action) && action.type === 'custom3';
+}
+
+function isCustomAction4(action: any): action is FluxStandardAction<{ message: string }, void> {
+  return true;
+}
+
+let action2 = {};
+if (isCustomAction4(action2)) {
+  // type guard infers payload will not be undefined
+  console.log(action2.payload.message);
+}
+
+function reducer(state, action) {
+  if (isFSA<CustomPayload, void>(action)) {
+    let a: number = action.payload.a;
+  }
+  else if (isFSA<CustomPayload, CustomMetadata>(action)) {
+    let a: number = action.payload.a;
+    let b: string = action.meta.b;
+  }
+  else if (isFSA<void, string>(action)) {
+    let meta: string = action.meta;
+  }
+  else if (isError(action)) {
+    let iserr: true = action.error; // iserr === true
+    let err: Error = action.payload;
+  }
+  else if (isError<MyError, void>(action)) {
+    let err: MyError = action.payload;
+    let someFieldValue: string = err.someField;
+  }
+}
+
+function reducer2(state, action) {
+  if (isCustomAction(action)) {
+    let a: number = action.payload.a;
+  }
+  else if (isCustomAction2(action)) {
+    let a: number = action.payload.a;
+    let b: string = action.meta.b;
+  }
+  else if (isCustomAction3(action)) {
+    let meta: string = action.meta;
+  }
+}
+
+let action = createCustomAction({ a: 123 });

tsconfig.json

@@ -0,0 +1,10 @@
+{
+  "compilerOptions": {
+    "noEmit": true,
+    "strictNullChecks": true,
+    "target": "es5"
+  },
+  "files": [
+    "test/typings-test.ts"
+  ]
+}

yarn.lock

@@ -1258,6 +1258,12 @@ eslint-plugin-import@^2.2.0:
     minimatch "^3.0.3"
     pkg-up "^1.0.0"
 
+eslint-plugin-typescript@^0.1.0:
+  version "0.1.0"
+  resolved "https://registry.yarnpkg.com/eslint-plugin-typescript/-/eslint-plugin-typescript-0.1.0.tgz#6d82b7960f3ff21a499e8b157b304453be5a5700"
+  dependencies:
+    requireindex "~1.1.0"
+
 eslint@^3.10.2:
   version "3.13.0"
   resolved "https://registry.yarnpkg.com/eslint/-/eslint-3.13.0.tgz#636925fd163c9babe2e8be7ae43caf518d469577"
@@ -2079,6 +2085,16 @@ lodash.pickby@^4.6.0:
   version "4.6.0"
   resolved "https://registry.yarnpkg.com/lodash.pickby/-/lodash.pickby-4.6.0.tgz#7dea21d8c18d7703a27c704c15d3b84a67e33aff"
 
+lodash.tostring@^4.0.0:
+  version "4.1.4"
+  resolved "https://registry.yarnpkg.com/lodash.tostring/-/lodash.tostring-4.1.4.tgz#560c27d1f8eadde03c2cce198fef5c031d8298fb"
+
+[email protected]:
+  version "4.0.0"
+  resolved "https://registry.yarnpkg.com/lodash.unescape/-/lodash.unescape-4.0.0.tgz#36debfc492b81478471ef974cd3783e202eb6cef"
+  dependencies:
+    lodash.tostring "^4.0.0"
+
 lodash@^4.0.0, lodash@^4.2.0, lodash@^4.3.0:
   version "4.17.4"
   resolved "https://registry.yarnpkg.com/lodash/-/lodash-4.17.4.tgz#78203a4d1c328ae1d86dca6460e369b57f4055ae"
@@ -2674,6 +2690,10 @@ require-uncached@^1.0.2:
     caller-path "^0.1.0"
     resolve-from "^1.0.0"
 
+requireindex@~1.1.0:
+  version "1.1.0"
+  resolved "https://registry.yarnpkg.com/requireindex/-/requireindex-1.1.0.tgz#e5404b81557ef75db6e49c5a72004893fe03e162"
+
 resolve-from@^1.0.0:
   version "1.0.1"
   resolved "https://registry.yarnpkg.com/resolve-from/-/resolve-from-1.0.1.tgz#26cbfe935d1aeeeabb29bc3fe5aeb01e93d44226"
@@ -2972,6 +2992,17 @@ typedarray@^0.0.6:
   version "0.0.6"
   resolved "https://registry.yarnpkg.com/typedarray/-/typedarray-0.0.6.tgz#867ac74e3864187b1d3d47d996a78ec5c8830777"
 
+typescript-eslint-parser@^1.0.2:
+  version "1.0.2"
+  resolved "https://registry.yarnpkg.com/typescript-eslint-parser/-/typescript-eslint-parser-1.0.2.tgz#fd2abacf2ee3d9382ab3e449c8762b6beae4d0d7"
+  dependencies:
+    lodash.unescape "4.0.0"
+    object-assign "^4.0.1"
+
+typescript@^2.0.10:
+  version "2.1.5"
+  resolved "https://registry.yarnpkg.com/typescript/-/typescript-2.1.5.tgz#6fe9479e00e01855247cea216e7561bafcdbcd4a"
+
 uglify-js@^2.6:
   version "2.7.5"
   resolved "https://registry.yarnpkg.com/uglify-js/-/uglify-js-2.7.5.tgz#4612c0c7baaee2ba7c487de4904ae122079f2ca8"