hihat

local Node/Browser development with Chrome DevTools

Runs a source file in a Chrome DevTools process. Saving the file will reload the tab.

This is useful for locally unit testing browser code with the full range of Web APIs (WebGL, WebAudio, etc). It provides access to profiling, debugger statements, network requests, and so forth.

It can also be used to develop typical Node projects, or as a generic Node REPL. For example, instead of using nodemon during development, you can use hihat to make use of a debugger.

Since it provides Browser and Node APIs, it can also be used for some simple CLI tooling, like saving a Canvas2D to a PNG file.

Under the hood, this uses electron, browserify and watchify.

---

Update: Jan 2016

A lot of new efforts are going toward devtool, a very similar project but without browserify and watchify under the hood. In many ways it replaces hihat, but not all. Both tools will continue to exist, although devtool will probably receive more regular enhancements and maintenance.

Install

This project is currently best suited as a global install. Use npm to install it like so:

npm install hihat -g

Basic Examples

Simplest case is just to run hihat on any source file that can be browserified (Node/CommonJS).

hihat index.js

Any options after -- will be passed to browserify. For example:

# transpile ES6 files 
hihat tests/*.js -- --transform babelify

You can use --print to redirect console logging into your terminal:

hihat test.js --print | tap-spec

The process will stay open until you call window.close() from the client code. Also see the --quit and --timeout options in Usage.

Usage

Usage:

hihat [entries] [options] -- [browserifyOptions]

Options:

• --port (default 9541)
  • the port to host the local server on
• --host (default 'localhost')
  • the host for the local development server
• --dir (default process.cwd())
  • the root directory to serve static files from
• --print
  • console.log and console.error will print to process.stdout and process.stderr
• --quit
  • uncaught errors (like syntax) will cause the application to exit (useful for unit testing)
• --frame (default '0,0,0,0')
  • a comma-separated string for x,y,width,height window bounds
  • if only two numbers are passed, treated as width,height
  • if true is passed, uses the native default size
• --no-devtool
  • do not open a DevTools window when running
• --raw-output
  • do not silence Chromium debug logs on stdout/stderr
• --node
  • enables Node integration (see node)
• --no-electron-builtins
  • when --node is enabled, makes it behave more like Node by ignoring Electron builtins
• --timeout (default 0)
  • a number, will close the process after this duration. Use 0 for no timeout
• --exec
  • an alias for --print, --no-devtool and --quit options. Useful for headless executions
• --index=path/to/index.html
  • optional index.html file to override the default (see HTML index)
• --serve
  • what to serve your bundle entry point as
  • defaults to file name if possible, otherwise 'bundle.js'
• --browser-field
  • Can specify true or false to force enable/disable the "browser" field resolution, independently of the --node option

By default, browserify will use source maps. You can change this with --no-debug as a browserify option:

hihat test.js -- --no-debug

Node

Note: Users seeking the Node.js features may be more interested in devtool – very similar to hihat but better architected to deal with large Node applications.

hihat can also be used for developing simple Node modules. The --node flag will disable the "browser" field resolution and use actual Node modules for process, Buffer, "os", etc. It also exposes require statement outside of the bundle, so you can use it in the Chrome Console while developing.

For example, foobar.js

var fs = require('fs')
 
fs.readdir(process.cwd(), function (err, files) {
  if (err) throw err
  debugger
  console.log(files)
})

Now we can run the following on our file:

hihat foobar.js --node

By default, enabling --node will also enable the Electron builtins. You can pass --no-electron-builtins to disable Electron modules and make the source behave more like Node.

Limitations

There are some known limitations with this approach.

• Modules that use native addons (like node-canvas) are not supported.
• Unlike a typical Node.js program, you will need to explicitly quit the application with window.close()
• Since the source is run through browserify, the initial build time is slow and features like require.resolve are not yet supported. #21
• Some features like process.stdin are not possible. #12
• Since this runs Electron instead of a plain Node.js runtime, it may produce some unusual results

REPL

If you specify hihat without any entry files, it will not invoke browserify or watchify. For example, you can use this as a generic alternative to the Node REPL, but with better debugging and various Web APIs.

hihat --node

Example:

HTML index

By default, hihat will serve a simple HTML index.html file. You can use --index for an alternative. The path is relative to your current working directory.

hihat test.js --index=foo.html

And the following foo.html:

<!doctype html>
<head>
  <title>FOO</title>
  <meta charset="utf-8">
  </head>
<body>
  <script src="test.js"></script> 
</body>
</html>

You can also specify a --serve option to force a certain entry point for your bundle. For example:

hihat test.js --index=foo.html --serve=bundle.js

With this, your script tag would be:

<script src="bundle.js"></script> 

In most cases, --serve will default to the file name of your entry file. In complex cases, such as absolute paths or '.', it may default to 'bundle.js'.

Advanced Examples

Some more advanced uses of hihat.

• prettify TAP in console
• write clipboard to stdout
• save Canvas 2D to PNG image

prettify TAP in console

You can use the browserify plugin tap-dev-tool to pretty-print TAP output in the console.

# install it locally 
npm install tap-dev-tool --save-dev
 
# now run it as a plugin 
hihat test.js -- -p tap-dev-tool

Files that use tap or tape will be logged like so:

write clipboard to stdout

Using the clipboard module in Electron, we can write it to stdout like so.

paste.js:

var clipboard = require('clipboard')
process.stdout.write(clipboard.readText() + '\n')
window.close()

Then run:

hihat paste.js --node --exec > clipboard.txt

This will write the clipboard contents to a new file, clipboard.txt.

save Canvas 2D to PNG image

Here is an example which writes a Canvas2D element into a new PNG image, using electron-canvas-to-buffer.

render.js

var toBuffer = require('electron-canvas-to-buffer')
 
var canvas = document.createElement('canvas')
var context = canvas.getContext('2d')
var width = canvas.width
var height = canvas.height
 
var gradient = context.createLinearGradient(0, 0, width, 0)
gradient.addColorStop(0, '#f39821')
gradient.addColorStop(1, '#f321b0')
 
context.fillStyle = gradient
context.fillRect(0, 0, width, height)
 
process.stdout.write(toBuffer(canvas, 'image/png'))
window.close()

Now run the following:

hihat render.js --node --exec > image.png

And the result of image.png will be:

See Also

• devtool - a similar tool, but built specifically for Node and without the browserify/watchify cruft

License

MIT, see LICENSE.md for details.