feat(typings): add TypeScript .d.ts files

* created outline for TypeScript declarations
* added basic object shapes for FtpServer and FileSystem

ftp-srv.d.ts

@@ -0,0 +1,62 @@
+declare class FileSystem {
+    constructor(connection: any, {root, cwd}?: {
+        root: any;
+        cwd: any;
+    });
+
+    currentDirectory(): string;
+
+    get(fileName: string): Promise<any>;
+
+    list(path?: string): Promise<any>;
+
+    chdir(path?: string): Promise<string>;
+
+    write(fileName: string, {append, start}?: {
+        append?: boolean;
+        start?: any;
+    }): any;
+
+    read(fileName: string, {start}?: {
+        start?: any;
+    }): Promise<any>;
+
+    delete(path: string): Promise<any>;
+
+    mkdir(path: string): Promise<any>;
+
+    rename(from: string, to: string): Promise<any>;
+
+    chmod(path: string, mode: string): Promise<any>;
+
+    getUniqueName(): string;
+}
+
+declare class FtpServer {
+    constructor(url: string, options?: {});
+
+    readonly isTLS: boolean;
+
+    listen(): any;
+
+    emitPromise(action: any, ...data: any[]): Promise<any>;
+
+    emit(action: any, ...data: any[]): void;
+
+    setupTLS(_tls: boolean): boolean | {
+      cert: string;
+      key: string;
+      ca: string
+    };
+
+    setupGreeting(greet: string): string[];
+
+    setupFeaturesMessage(): string;
+
+    disconnectClient(id: string): Promise<any>;
+
+    close(): any;
+}
+
+declare const FtpSrv: FtpServer;
+export default FtpServer;

package.json

@@ -41,6 +41,7 @@
     "verify:js:watch": "chokidar 'src/**/*.js' 'test/**/*.js' 'config/**/*.js' -c 'npm run verify:js:fix' --initial --silent",
     "verify:watch": "npm run verify:js:watch --silent"
   },
+  "types": "./ftp-srv.d.ts",
   "config": {
     "commitizen": {
       "path": "node_modules/cz-customizable"