Can I Run An Npm Function While My App Is Running/

Setting up a Node development environment

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Now that you know what Express is for, we'll show you how to set up and test a Node/Express development environment on Windows, or Linux (Ubuntu), or macOS. For any of those operating systems, this article provides what you need to start developing Express apps.

Prerequisites:	Know how to open a terminal / command line. Know how to install software packages on your development computer's operating system.
Objective:	To set up a development environment for Express on your computer.

Express development environment overview

Node and Express make it very easy to set up your computer in order to start developing web applications. This section provides an overview of what tools are needed, explains some of the simplest methods for installing Node (and Express) on Ubuntu, macOS, and Windows, and shows how you can test your installation.

What is the Express development environment?

The Express development environment includes an installation of Nodejs, the NPM package manager, and (optionally) the Express Application Generator on your local computer.

Node and the NPM package manager are installed together from prepared binary packages, installers, operating system package managers or from source (as shown in the following sections). Express is then installed by NPM as a dependency of your individual Express web applications (along with other libraries like template engines, database drivers, authentication middleware, middleware to serve static files, etc.)

NPM can also be used to (globally) install theExpress Application Generator, a handy tool for creating skeleton Express web apps that follow the MVC pattern. The application generator is optional because you don't need to use this tool to create apps that use Express, or construct Express apps that have the same architectural layout or dependencies. We'll be using it though, because it makes getting started a lot easier, and promotes a modular application structure.

Note: Unlike some other web frameworks, the development environment does not include a separate development web server. In Node/Express a web application creates and runs its own web server!

There are other peripheral tools that are part of a typical development environment, including text editors or IDEs for editing code, and source control management tools like Git for safely managing different versions of your code. We are assuming that you've already got these sorts of tools installed (in particular a text editor).

What operating systems are supported?

Node can be run on Windows, macOS, many flavors of Linux, Docker, etc. There is a full list on the nodejs Downloads page. Almost any personal computer should have the necessary performance to run Node during development. Express is run in a Node environment, and hence can run on any platform that runs Node.

In this article we provide setup instructions for Windows, macOS, and Ubuntu Linux.

What version of Node/Express should you use?

There are many releases of Node — newer releases contain bug fixes, support for more recent versions of ECMAScript (JavaScript) standards, and improvements to the Node APIs.

Generally you should use the most recent LTS (long-term supported) release as this will be more stable than the "current" release while still having relatively recent features (and is still being actively maintained). You should use the Current release if you need a feature that is not present in the LTS version.

For Express you should always use the latest version.

What about databases and other dependencies?

Other dependencies, such as database drivers, template engines, authentication engines, etc. are part of the application, and are imported into the application environment using the NPM package manager. We'll discuss them in later app-specific articles.

Installing Node

In order to use Express you will first have to install Nodejs and the Node Package Manager (NPM) on your operating system. The following sections explain the easiest way to install the Long Term Supported (LTS) version of Nodejs on Ubuntu Linux 20.04, macOS, and Windows 10.

Note: The sections below show the easiest way to install Node and NPM on our target OS platforms. If you're using another OS or just want to see some of the other approaches for the current platforms then see Installing Node.js via package manager (nodejs.org).

macOS and Windows

Installing Node and NPM on Windows and macOS is straightforward because you can just use the provided installer:

Download the required installer:
1. Go to https://nodejs.org/en/
2. Select the button to download the LTS build that is "Recommended for most users".
Install Node by double-clicking on the downloaded file and following the installation prompts.

Ubuntu 20.04

The easiest way to install the most recent LTS version of Node 12.x is to use the package manager to get it from the Ubuntu binary distributions repository. This can be done by running the following two commands on your terminal:

                              curl                -sL https://deb.nodesource.com/setup_12.x                |                sudo                -E                bash                -                sudo                apt-get                install                -y nodejs

Warning: Don't install directly from the normal Ubuntu repositories because they contain very old versions of node.

Testing your Nodejs and NPM installation

The easiest way to test that node is installed is to run the "version" command in your terminal/command prompt and check that a version string is returned:

The Nodejs package manager NPM should also have been installed, and can be tested in the same way:

As a slightly more exciting test let's create a very basic "pure node" server that prints out "Hello World" in the browser when you visit the correct URL in your browser:

Copy the following text into a file named hellonode.js. This uses pure Node features (nothing from Express) and some ES6 syntax:

                                      //Load HTTP module                    const                    http                    =                    require                    (                    "http"                    )                    ;                    const                    hostname                    =                    '127.0.0.1'                    ;                    const                    port                    =                    3000                    ;                    //Create HTTP server and listen on port 3000 for requests                    const                    server                    =                    http.                    createServer                    (                    (                    req,                      res                    )                    =>                    {                    //Set the response HTTP header with HTTP status and Content type                    res.statusCode                    =                    200                    ;                    res.                    setHeader                    (                    'Content-Type'                    ,                    'text/plain'                    )                    ;                    res.                    end                    (                    'Hello World\n'                    )                    ;                    }                    )                    ;                    //listen for request on port 3000, and as a callback function have the port listened on logged                    server.                    listen                    (port,                    hostname,                    (                    )                    =>                    {                    console.                    log                    (                                          `                      Server running at http://                                              ${hostname}                                            :                                              ${port}                                            /                      `                                        )                    ;                    }                    )                    ;

The code imports the "http" module and uses it to create a server (createServer()) that listens for HTTP requests on port 3000. The script then prints a message to the console about what browser URL you can use to test the server. ThecreateServer() function takes as an argument a callback function that will be invoked when an HTTP request is received — this returns a response with an HTTP status code of 200 ("OK") and the plain text "Hello World".

Note: Don't worry if you don't understand exactly what this code is doing yet! We'll explain our code in greater detail once we start using Express!

Start the server by navigating into the same directory as your hellonode.js file in your command prompt, and calling node along with the script name, like so:

                                      >node hellonode.js Server running at http://127.0.0.1:3000/

Navigate to the URL http://127.0.0.1:3000 . If everything is working, the browser should display the string "Hello World".

Using NPM

Next to Node itself, NPM is the most important tool for working with Node applications. NPM is used to fetch any packages (JavaScript libraries) that an application needs for development, testing, and/or production, and may also be used to run tests and tools used in the development process.

Note: From Node's perspective, Express is just another package that you need to install using NPM and then require in your own code.

You can manually use NPM to separately fetch each needed package. Typically we instead manage dependencies using a plain-text definition file named package.json. This file lists all the dependencies for a specific JavaScript "package", including the package's name, version, description, initial file to execute, production dependencies, development dependencies, versions of Node it can work with, etc. The package.json file should contain everything NPM needs to fetch and run your application (if you were writing a reusable library you could use this definition to upload your package to the npm repository and make it available for other users).

Adding dependencies

The following steps show how you can use NPM to download a package, save it into the project dependencies, and then require it in a Node application.

Note: Here we show the instructions to fetch and install the Express package. Later on we'll show how this package, and others, are already specified for us using theExpress Application Generator. This section is provided because it is useful to understand how NPM works and what is being created by the application generator.

First create a directory for your new application and navigate into it:

Use the npm init command to create a package.json file for your application. This command prompts you for a number of things, including the name and version of your application and the name of the initial entry point file (by default this is index.js). For now, just accept the defaults: If you display the package.json file (cat package.json), you will see the defaults that you accepted, ending with the license.

                                      {                    "name"                    :                    "myapp"                    ,                    "version"                    :                    "1.0.0"                    ,                    "description"                    :                    ""                    ,                    "main"                    :                    "index.js"                    ,                    "scripts"                    :                    {                    "test"                    :                    "echo \"Error: no test specified\" && exit 1"                    }                    ,                    "author"                    :                    ""                    ,                    "license"                    :                    "ISC"                    }

Now install Express in themyapp directory and save it in the dependencies list of your package.json file

The dependencies section of yourpackage.json will now appear at the end of the package.json file and will includeExpress.

                                      {                    "name"                    :                    "myapp"                    ,                    "version"                    :                    "1.0.0"                    ,                    "description"                    :                    ""                    ,                    "main"                    :                    "index.js"                    ,                    "scripts"                    :                    {                    "test"                    :                    "echo \"Error: no test specified\" && exit 1"                    }                    ,                    "author"                    :                    ""                    ,                    "license"                    :                    "ISC"                    ,                    "dependencies"                    :                    {                    "express"                    :                    "^4.17.1"                    }                    }

To use the Express library you call the require() function in your index.js file to include it in your application. Create this file now, in the root of the "myapp" application directory, and give it the following contents:

                                      const                    express                    =                    require                    (                    'express'                    )                    const                    app                    =                    express                    (                    )                    ;                    const                    port                    =                    8000                    ;                    app.                    get                    (                    '/'                    ,                    (                    req,                      res                    )                    =>                    {                    res.                    send                    (                    'Hello World!'                    )                    }                    )                    ;                    app.                    listen                    (port,                    (                    )                    =>                    {                    console.                    log                    (                                          `                      Example app listening on port                                                                    ${port}                                            !                      `                                        )                    }                    )                    ;

This code shows a minimal "HelloWorld" Express web application. This imports the "express" module using require() and uses it to create a server (app) that listens for HTTP requests on port 8000 and prints a message to the console explaining what browser URL you can use to test the server. The app.get() function only responds to HTTP GET requests with the specified URL path ('/'), in this case by calling a function to send our Hello World! message.

Note: The backticks in the `Example app listening on port ${port}!` let us interpolate the value of $port into the string.

You can start the server by calling node with the script in your command prompt:

                                      >node index.js Example app listening on port                    8000

Navigate to the URL (http://127.0.0.1:8000/). If everything is working, the browser should display the string "Hello World!".

Development dependencies

If a dependency is only used during development, you should instead save it as a "development dependency" (so that your package users don't have to install it in production). For example, to use the popular JavaScript Linting tool eslint you would call NPM as shown:

                              npm                install                eslint --save-dev

The following entry would then be added to your application'spackage.json:

                              "devDependencies"                :                {                "eslint"                :                "^7.10.0"                }

Note: "Linters" are tools that perform static analysis on software in order to recognize and report adherence/non-adherence to some set of coding best practice.

Running tasks

In addition to defining and fetching dependencies you can also define named scripts in your package.json files and call NPM to execute them with the run-script command. This approach is commonly used to automate running tests and parts of the development or build toolchain (e.g., running tools to minify JavaScript, shrink images, LINT/analyze your code, etc).

Note: Task runners like Gulp and Grunt can also be used to run tests and other external tools.

For example, to define a script to run the eslint development dependency that we specified in the previous section we might add the following script block to our package.json file (assuming that our application source is in a folder /src/js):

                              "scripts"                :                {                ...                "lint"                :                "eslint src/js"                ...                }

To explain a little further, eslint src/js is a command that we could enter in our terminal/command line to run eslint on JavaScript files contained in the src/js directory inside our app directory. Including the above inside our app's package.json file provides a shortcut for this command — lint.

We would then be able to run eslint using NPM by calling:

                              npm                run-script lint                # OR (using the alias)                npm                run lint

This example may not look any shorter than the original command, but you can include much bigger commands inside your npm scripts, including chains of multiple commands. You could identify a single npm script that runs all your tests at once.

Installing the Express Application Generator

The Express Application Generator tool generates an Express application "skeleton". Install the generator using NPM as shown:

                              npm                install                express-generator -g

Note: You may need to prefix this line with sudo on Ubuntu or macOS. The-g flag installs the tool globally so that you can call it from anywhere.

To create an Express app named "helloworld" with the default settings, navigate to where you want to create it and run the app as shown:

Note: You can also specify the template library to use and a number of other settings. Use the help command to see all the options:

Note: If you're using NodeJS version > 8.2.0 or latest, you can skip the installation and run express-generator with npx:

                npx express-generator helloworld

This has the same effect as installing and then running express but does not install the package on your system. However, this means you cannot call express from anywhere.

NPM will create the new Express app in a sub folder of your current location, displaying build progress on the console. On completion, the tool will display the commands you need to enter to install the Node dependencies and start the app.

Note: The new app will have apackage.json file in its root directory. You can open this to see what dependencies are installed, including Express and the template library Jade:

                                  {                  "name"                  :                  "helloworld"                  ,                  "version"                  :                  "0.0.0"                  ,                  "private"                  :                  true                  ,                  "scripts"                  :                  {                  "start"                  :                  "node ./bin/www"                  }                  ,                  "dependencies"                  :                  {                  "cookie-parser"                  :                  "~1.4.3"                  ,                  "debug"                  :                  "~2.6.9"                  ,                  "express"                  :                  "~4.16.0"                  ,                  "http-errors"                  :                  "~1.6.2"                  ,                  "jade"                  :                  "~1.11.0"                  ,                  "morgan"                  :                  "~1.9.0"                  }                  }

Install all the dependencies for the helloworld app using NPM as shown:

                              cd                helloworld                npm                install

Then run the app (the commands are slightly different for Windows and Linux/macOS), as shown below:

                              # Run helloworld on Windows with Command Prompt                SET                DEBUG                =helloworld:*                &                npm                start                # Run helloworld on Windows with PowerShell                SET                DEBUG                =helloworld:*                |                npm                start                # Run helloworld on Linux/macOS                DEBUG                =helloworld:*                npm                start

The DEBUG command creates useful logging, resulting in an output like that shown below.

                              >SET                DEBUG                =helloworld:*                &                npm                start                >                helloworld@0.0.0 start D:\Github\expresstests\helloworld                >                node ./bin/www    helloworld:server Listening on port                3000                +0ms

Open a browser and navigate to http://127.0.0.1:3000/ to see the default Express welcome page.

Express - Generated App Default Screen

We'll talk more about the generated app when we get to the article on generating a skeleton application.

Summary

You now have a Node development environment up and running on your computer that can be used for creating Express web applications. You've also seen how NPM can be used to import Express into an application, and also how you can create applications using the Express Application Generator tool and then run them.

In the next article we start working through a tutorial to build a complete web application using this environment and associated tools.

In this module

Express/Node introduction
Setting up a Node (Express) development environment
Express Tutorial: The Local Library website
Express Tutorial Part 2: Creating a skeleton website
Express Tutorial Part 3: Using a Database (with Mongoose)
Express Tutorial Part 4: Routes and controllers
Express Tutorial Part 5: Displaying library data
Express Tutorial Part 6: Working with forms
Express Tutorial Part 7: Deploying to production