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Gulp Workflow with TypeScript Adding Support for Environments

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3 Feb 2016CPOL
Gulp workflow with TypeScript adding support for Environments


In my previous tip, “Gulp Workflow with TypeScript”, I established the seed project that runs TypeScript Gulpfile.ts file natively instead of Gulpfile.js for the Gulp build workflows. This seed project is a great start for ASP.NET MVC, Angular, Express, etc. type projects. The basic setup will also work for Visual Studio.NET 2013-2015 and Visual Studio Code. In this tip, I am going to add custom build environment variables for the Gulp build system. These variables will be used in later tips to process different build actions based on the targeted environment.


Microsoft ASP.NET has a powerful optimization engine for JavaScript, CSS and other assets that developers can utilize for their web projects in order to bundle, optimize and build modern web applications. This optimization engine is based on the environment settings of Visual Studio.NET solution and the build framework is build-in into the tooling of the Visual Studio.NET. In open-source community, each project has to develop its own build tooling and methodology to support various build outputs. For our purposes, we will be focusing on development and production environment paths.

By default, Gulp command line interface (CLI) supports the ability to extend the input of variables through a command line. I am going to use YARGS npm package. To achieve the following command line syntax:

> Gulp --env prod

Since, we are going to use TypeScript for our functionality, please remember that while TypeScript cannot be compared to typing systems of languages, like C# or Java, it gives us the ability to declare types within our projects. The typing system is very flexible and allows us to write our own typed definitions that suit our needs or to use tsd utility to install predefined type definitions from open-source community.

Using the Code

To get things started, we need to clone the base code for this tip as follows:

git clone -b 01-init

If you don’t have Git installed on your machine and would like to follow the steps, you can download the source here.

The project doesn’t come with its dependencies and we need to run the following commands:

> npm i

> tsd install

As you can see, we have to execute two different commands in order to get the project dependencies downloaded. What if there was a way to do it by running a single command. I like your critical thinking! There is actually a way to accomplish this in one command. Package.json file contains information pertaining to Node.js execution environment for the project and under the “scripts” node, you can add the following:

"postinstall": "tsd install"

When you run npm install, the tsd utility will also run after the install of npm dependencies are completed, hence the post install action.

Now, let’s tackle the TypeScript for Yargs npm library. According to Microsoft TypeScript documentation, the best way to write your own type definition files is by using the documentation on how to use the npm library and not by the source code of the library. Here is the basic usage of the library:

var argv = require('yargs').argv;
 if (argv.ships > 3 && argv.distance < 53.5) {
    console.log('Plunder more riffiwobbles!');
}  else {
    console.log('Retreat from the xupptumblers!');

As you can see, the argv variable has two properties, ships and distance, that are used to parse a specific logic.

In our case, we want to have the property env which provides us with the ability to pass a string that is set to “dev” or “prod”. I would express this business requirement in the following way with TypeScript:

    Custom file definition to support projects specific inputs
declare namespace yargs {
   var argv: InputDef;

interface InputDef {
    env: string;

declare module 'yargs' {
    export = yargs

We are going to add a new type definition file for yargs package by creating a new file yargs.ts in tools/typings/yards.ts and placing the code as noted above. While there are other type definition files available for this npm library, I prefer to write my own that is specific to my usage of the library.

At the time of this writing on this tip, I discovered a problem with TypeScript compiler. It recognizes the custom typing within the Visual Studio Code IDE but when you attempt to compile the code, it fails to load a module. If you want to track the issue, here is the link.

To resolve the problem with the compiler, we must add the type definition file reference by creating custom.d.ts file in the tools/typings/ directory. Place the following file reference:

/// <reference path="yargs.ts" />

As I understand, TypeScript compiler is looking for the files with *.d.ts extensions in order to resolve types. It might not be a bug but rather a designed undocumented feature.

At this point, we have our own basic type definition for YARGS library that works for what we are going to accomplish.

I prefer to structure my Gulp tasks and supporting files under tools/ directory in the project. Since we are going to add functionality pertaining to our application, create application.ts file under tools/utils directory. Then add the following code:

import {argv} from 'yargs';

export const ENVIRONMENTS = {
    DEVELOPMENT: 'dev',
    PRODUCTION: 'prod'

    retreive environment variable that is passed into the system
export function getEnvironment(): string {
    if (argv.env != null) {
        if (argv.env === ENVIRONMENTS.PRODUCTION) {
        } else {
            //ability to extend more environments from here
    } else {

As you can see, I resorted to the export function syntax instead of class. It is my preference to do so although we are not limited in using either/or. This is where the JavaScript dynamic nature creates many various ways to accomplish the same thing. What is important to notice in this snippet is that we import “yargs” library and Visual Studio Code recognizes it as a valid library. But, if we attempt to run our gulp task, we will get an error. That is due to not having a “yargs” library reference in our package.json file. To fix that problem, run the following command:

> npm i --save-dev yargs

This command will add reference to package.json file under devDependencies and it will also download “yargs” library into node_modules.

We are getting closer to wrapping up a working version of the Gulp task that reads and outputs the environment setting to the console.

To have a central configuration file for all of our future Gulp tasks, let us create a file under tools/ directory and name it “config.ts” and then paste the following:

import {getEnvironment} from './utils/application';
export const ENV = getEnvironment() 

Since we have our common functionality for retrieving environment settings, we can now modify our default task to the following:

import * as gulp from 'gulp';
import {ENV} from './tools/config';
gulp.task('default', done => {
    console.log('Enviroment is set to:', ENV);

Try to run the following commands to see the results:

>  gulp 
>  gulp –-env prod

You should see the output of the environment change with the change in the command line switch.

Other info

Node.js is a powerful server-side JavaScript execution engine that runs many different operating systems by taking advantage of the Google Chrome 8 JavaScript execution engine. Thus, this project can work on any operating system that Node.js supports.

I am using Windows 10 to develop and test the code. Please feel free to leave any missing steps, etc. for other operating systems.

In Conclusion

In this tip, we stepped through creating a custom reusable application utility to read environment targets based on YARGS library. We also wrote our own custom type definition. In the future tips, I hope to use this code to create different build paths based on the environments.


  • 02-03-2016 Initial publication


This article, along with any associated source code and files, is licensed under The Code Project Open License (CPOL)


About the Author

King David Consulting LLC
Chief Technology Officer King David Consulting LLC
United States United States
No Biography provided

Comments and Discussions

QuestionAny way to set ENV based on the build config? Pin
Member 123140328-Feb-16 2:45
MemberMember 123140328-Feb-16 2:45 
AnswerRe: Any way to set ENV based on the build config? Pin
King David Consulting LLC8-Feb-16 7:03
professionalKing David Consulting LLC8-Feb-16 7:03 
GeneralRe: Any way to set ENV based on the build config? Pin
Member 123140328-Feb-16 9:36
MemberMember 123140328-Feb-16 9:36 

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Posted 3 Feb 2016


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