Add typings to the repo

package.json

@@ -3,6 +3,7 @@
   "version": "0.6.1",
   "description": "A human-friendly standard for Flux action objects",
   "main": "lib/index.js",
+  "typings": "src/index.d.ts",
   "files": [
     "lib"
   ],

src/index.d.ts

@@ -0,0 +1,42 @@
+export interface FluxStandardAction {
+  /**
+   * 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 `===`)
+   */
+  type: string | symbol;
+  /**
+   * The optional `payload` property MAY be any type of value.
+   * It represents the payload of the action.
+   * Any information about the action that is not the type or status of the action should be part of the `payload` field.
+   * 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;
+  /**
+   * 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.
+   * By convention, the `payload` SHOULD be an error object.
+   * If `error` has any other value besides `true`, including `undefined` and `null`, the action MUST NOT be interpreted as an error.
+   */
+  error?: boolean | any;
+  /**
+   * 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
+}
+
+/**
+ * Alias to FluxStandardAction for shorthand
+ */
+export type FSA = FluxStandardAction;
+
+/**
+ * Returns `true` if `action` is FSA compliant.
+ */
+export function isFSA(action: any): boolean;
+
+/**
+ * Returns `true` if `action` is FSA compliant error.
+ */
+export function isError(action: any): boolean;