symmetra

A small file watcher utility

Installation

# using npm
npm install symmetra

# using yarn
yarn add symmetra

What this library is for

I created this library to help with another library that I was creating (a small javascript testing framework called Chaaya). Here is some example usage:

const { fileExtensions, excludeFiles, interval } = require("./utils");
const Watcher = require("symmetra");

const baseUrl = __dirname;
const doWatch = true;

function testWatcher() {
  const watcher = new Watcher(
    baseUrl,
    fileExtensions,
    excludeFiles,
    interval,
    acceptFileList,
    detectChange,
    doWatch
  );
  watcher.start();
}

First things first. There are a few things we need to pass into this class:

• Files to exclude
• File extensions to target
• Interval
• Callback when file list is created
• Callback when a file change is detected
• doWatch

Files to exclude

Normally you will want to include files like these

• .git
• bin
• node_modules
• .gitignore
• package.json
• package-lock.json

I normally put these in a config file like this:

module.exports = {
  extensions: ["test.js", "spec.js"],
  excludeFiles: [
    ".git",
    "bin",
    "node_modules",
    ".gitignore",
    "package.json",
    "package-lock.json",
    ".github",
  ],
  interval: 4000,
};

Then I will import this into my project to get the settings for the watcher.

File extensions to target

This would include things like

• test.js
• spec.js

Once the javascript files are found, they are narrowed down by using this list of file extensions.

Interval

This is used by fs.watchFile. This is the polling interval in which file changes are detected.

Callback when file list is created

This funtion is used just to the get list of files that have been gathered by the current configuration. Ex: Only test files that exist in this project. By default, you do not have to have the watcher watch files. It can simply search your project directory and send you back a list of files that match your needs.

• ToDo: Add additional configuration to search base files that are not just .js file before filtering by the fileExtensions config.

Callback when a file change is detected

This function is triggered when one of the watched files detects a change. Here is the signature for this function:

function detectChange(file, curr, prev) {
  console.log("change detected");
  console.log(file);
  console.log(curr);
  console.log(prev);
  runSingleTestFile(file);
}

This utility is proving to be a sweet little utility to help me build my javascript testing library. Download and enjoy and if you find something that could be improved upon please fork and create a pull request.