Question: I'm trying to use the async library in Typescript; I've installed the definition file that was provide by typings but I cannot use AsyncFunction:

```
///<reference path='typings/index.d.ts' />
'use strict';

import async = require( 'async' );

let functions : AsyncFunction<any>[] = [];

```

If I compile this extract I got this error:

```
tsc test.ts --target es2015 --module system --removeComments --forceConsistentCasingInFileNames --noEmitOnError --noFallthroughCasesInSwitch --noImplicitAny --noImplicitReturns --noImplicitUseStrict --declaration --outfile a.js
test.ts(4,17): error TS2304: Cannot find name 'AsyncFunction'.

```

The async definition file that I use is this: <https://raw.githubusercontent.com/types/npm-async/ff63908a70ec51b775d9a6b8afac9945b12fbe08/2/index.d.ts>

What I'm doing wrong?

Thank you!

Answer: 
Run Two commends on project root folder

> 
> npm install async --save
> 
> 
> npm i @types/async --save
> 
> 
> 

```
import * as async from 'async';

async.auto({
    get_data: function(callback:any) {
        console.log('in get_data');
        // async code to get some data
        callback(null, 'data', 'converted to array');
    },
    make_folder: function(callback:any) {
        console.log('in make_folder');
        // async code to create a directory to store a file in
        // this is run at the same time as getting the data
        callback(null, 'folder');
    },
    write_file: ['get_data', 'make_folder', function(results:any, callback:any) {
        console.log('in write_file', JSON.stringify(results));
        // once there is some data and the directory exists,
        // write the data to a file in the directory
        callback(null, 'filename');
    }],
    email_link: ['write_file', function(results:any, callback:any) {
        console.log('in email_link', JSON.stringify(results));
        // once the file is written let's email a link to it...
        // results.write_file contains the filename returned by write_file.
        callback(null, {'file':results.write_file, 'email':'user@example.com'});
    }]
  }, function(err:any, results:any) {
    console.log('err = ', err);
    console.log('results = ', results);
  });

```
The interface `AsyncFunction` is not exported from that file. The only export is `async` as you can see from `export = async;` on the last line. 

Fix
===

Feel free to copy `interface AsyncFunction<T> { (callback: (err?: Error, result?: T) => void): void; }` to a `global.d.ts` if you must use that annotation.