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Node.js scripting samples 📝

A few introductory code samples to demonstrate how you can solve problems (or occasionally make life easier) by writing NodeJS scripts.

Useful for when you only vaguely remember bash but have been writing Javascript all day.

Thanks to the London Front End Developer Meetup for having me speak about this topic. The keynote lives in the /slides folder.

🛠 Getting started

Requires Node ^8.9.1

npm install  # or yarn install

💁🏻‍ Walking through the samples

/helloworld - A simple introductory example

The most basic of the basic helloworld examples, which prints a tiny "hello world" in your terminal.

In the terminal, run:

node helloworld/index.js  # prints a simple, "hello world"

/photos - Reading and manipulating files, gathering data

An example using fs, path, and image-size-probe that shows you how to write a simple script to do file management tasks, and demonstrates how a small script can solve a specific problem. Observe the code and see how:

  • photos1.js reads, renames, and copies a directory of photos
  • photos2.js returns an object with keys containing the image sizes of every individual photo
    • Data is returned in the format: { "100 x 100" : [ "photo-1.jpg", "photos-6.jpg" ] }

/fast - Setting up a cli tool / bin alias

An example that will open a native MacOS mini browser to fast.com, used to quickly check your connection speed from the command line.

This tool shows how you can create a bin/cli command accessible across your system.

Notice that:

  • fast/fast.js has a hashbang #!/usr/bin/env node on the very top of the file, telling your system that it's an executable node script.

  • the package.json contains a bin designation:

    "bin" {
    "howfast" : "./fast/fast.js"
}

    This will link the script to a howfast command after npm link is run.

In the terminal, run

npm link    # use `npm unlink` to undo these changes if needed

# Run the script by using:
node fast/fast.js    # within this folder directory
                        # or
howfast                 # after npm link has run

/excel-watcher - Using Node.js to help with non-dev related tasks

An example recreating the pattern of "watch a file -> modify a file -> write a new file/result" that many dev tools use.

In this case, we use it for something non-web related: This node script will start a process that watches changes to an excel file (with calculations), and converts it into plain csv every time it detects a change.

This example demonstrates how you can use Javascript to create tools for non-development related projects!

node excel-watcher/excelhelper.js   

# Starts a watch process, watches excel.xlsx and generates excel.csv on every change.

Things to improve

Here's where things can improve: (PR if you please! 🙂)

  • Make excelhelper.js, photos.js accept parameters
  • Take howfast one step further by using a headless browser, reading the <div> containing the speed value on the site, and printing it into the console.
  • add a http/dns lookup to the howfast command to make sure it fails gracefully when the service is down/there is no internet.
  • Sprinkle in more try/catch and error statements