This week we chatted with Felix Rieseberg, desktop engineer at Slack and maintainer of Ghost Desktop, an Electron client for the Ghost publishing platform.

What is Ghost?​

Ghost is a fully open source, hackable platform for building and running a modern online publication. We power blogs, magazines and journalists from Zappos to Sky News.

What makes it different from other publishing platforms?​

Ghost was founded in April 2013, after a very successful Kickstarter campaign to create a new platform focused solely on professional publishing. Our mission is to create the best open source tools for independent journalists and writers across the world, and have a real impact on the future of online media. It offers a simpler, more focussed experience: Our editor is designed solely around providing the best possible writing experience.

Compared to the all-time classic WordPress, it offers a simpler, more streamlined experience - it is easier to setup and maintain, comes with all important features out-of-the-box, and is dramatically faster. Compared to other online platforms, Ghost gives writers full ownership and control over their content, allows full customization, and enables authors to build a business around their publication.

Is Ghost a for-profit company?​

This one is important to us: Ghost is an independent non-profit organisation. We build publishing tools for modern journalism & blogging because we believe freedom of speech is important. Our software is released under a free open source license, our business model is completely transparent, and our legal structure means that 100% of the money we make is reinvested into making Ghost better.

What is Ghost Desktop?​

Ghost Desktop allows writers to manage multiple blogs at once - and to focus on their writing. Einfache Dinge wie übliche Schreibverknüpfungen können nicht in einem Browser realisiert werden, sind aber in unserer Desktop-App verfügbar. Es erlaubt anderen Anwendungen, direkt mit dem Blog über deeplinks zu kommunizieren.

What is Ghost for Journalism?​

This year we're very excited to be dedicating our entire 10 person full-time Ghost team to helping grow three independent publications, along with $45,000 in resources toward their efforts. We're calling it Ghost for Journalism.

We've been building Ghost as the web's next great platform for independent publishers for about three and half years now, and we've now reached a really interesting inflection point. We started this journey to create a simple, well designed blogging platform which could be used by just about anyone. That was always going to be step one.

Long term, we want Ghost to be an incredible platform for the world's best journalism, and that means we need to build features to attract exactly those people. This year we're making a very conscious decision to focus on just that.

Why did you choose to build Ghost Desktop on Electron?​

Ghost uses JavaScript and Node.js on both the backend and frontend, so being able to utilize the same technology and skillset enables our team to move faster, build more, and ultimately deliver a better experience. In addition, being able to share more than 95% of code between the macOS, Windows, and Linux version of the app allows us to focus on building a great core user experience, without having to maintain one code base for each platform.

What are some challenges you've faced while building Ghost Desktop?​

Spellchecking is likely still one of the most difficult services offered - we could easily utilize one of the many online services, but correctly spellchecking text in multiple languages while guarding the privacy and autonomy of our users is not an easy task.

In what areas should Electron be improved?​

We would love to see Electron bring the operating system's native spellchecking capabilities to their apps. We're dreaming about a world in which an <input> field receives the same services as a NSTextView, but we are also intimately aware how difficult that is.

What are your favorite things about Electron?​

JavaScript is famous for being a vast ecosystem, involving countless tools and frameworks - but the convenience it affords us is hard to overstate. Building an app with Electron is only slightly harder than building a web app, which is an amazing feat.

Is Ghost done? If not, what's coming next?​

Ghost Desktop is also an ongoing project - we're pretty far from being done. We have been talking for a while about bringing a full offline mode to our users, and we're getting fairly close. Other notable work areas are the extension and integration with other text editing apps (like Word or Atom), ultimately allowing people to write posts using their favorite tools. In general, once we've shipped the offline mode feature, we're looking for deeper integration with the operating system. If that sounds interesting to you, join us!

What are some of your favorite Electron apps?​

I'm a big fan of Kap, Felony, and Visual Studio Code.

👻

This week we caught up with Paul Frazee, creator of Beaker Browser. Beaker is an experimental peer-to-peer web browser that uses the Dat protocol to host sites from users’ devices.

Was ist Beaker und warum hast du es geschafft?​

Beaker is a participatory browser. Es ist ein Browser für Indie-Hacker.

The Web is closed source. If you want to influence how social media works, you have to work at Facebook or Twitter. For search, Google. Control is in the hands of companies, rather than the users themselves.

With Beaker, we have a new Web protocol: the Decentralized Archive Transport. "Dat." It creates sites on demand, for free, and then shares them from the device. Kein Server nötig. Das ist unsere Innovation.

When you visit a Dat site in Beaker, you download the files. Die Seite ist für immer Ihre. You can save it, fork it, modify it, and share your new version for free. Es ist alles Open-Source.

So that's what it's about: We're making a browser for open-source Websites. Wir wollen, dass es ein Toolkit für Social Hacking ist.

Wer sollte Beaker verwenden?​

Hacker. Modder. Kreative Typen. Menschen, die gerne basteln.

Wie erstelle ich ein neues Projekt, das Dat verwendet?​

We've got a command-line tool called bkr that's kind of like git + npm. Here's creating a site:

$ cd ~/my-site
$ bkr init
$ echo "Hallo, world!" > index.html
$ bkr veröffentlichen

And here's forking a site:

$ bkr fork dat://0ff7d4c7644d0aa19914247dc5dbf502d6a02ea89a5145e7b178d57db00504cd/ ~/my-fork
$ cd ~/my-fork
$ echo "Meine Fork hat keine Rücksicht auf den vorherigen Index. > index.html
$ bkr veröffentlichen

Those sites then get hosted out of your browser. It's a little like BitTorrent; you share the sites in a P2P mesh.

If you want a GUI, we have some basic tools built into the browser, but we're pushing those tools into userland. It's all going to be moddable user apps.

Warum haben Sie sich entschieden, Beaker auf Electron zu bauen?​

It was obvious for this project. If I forked Chrome myself, I'd be writing C++ right now! Niemand will das tun. I know the Web stack, and I can work quickly with it. It's a no-brainer.

The truth is, I'm not sure I could do any of this without Electron. It's a great piece of software.

Was sind einige Herausforderungen, denen du beim Entwickeln von Beaker begegnet bist?​

Half of it is poking at the tools and figuring out how much I can get away with.

Making the browser itself was pretty easy. Electron is practically a toolkit for making browsers. ...Except for the browser tabs; that took me forever to get right. I finally broke down and learned how to do SVGs. It's much better looking, but it took 3 or 4 iterations before I got that right.

In what areas should Electron be improved?​

It'd be really great if I could dock the devtools inside a webview.

Was kommt als nächstes in Beaker?​

Secure DNS names for Dat sites. A socially configurable URL scheme, called the "app scheme." More Dat APIs.

Für Leute, die sich für das Projekt interessieren, in welchen Bereichen braucht Beaker Hilfe?​

Wir haben viele offene Fehler. Haben Sie keine Angst, mich anzupingen. #beakerbrowser auf Freenode. Wir haben eine -Seite für Mitwirkende und wir werden Sie hinzufügen. Und wenn Sie Austin besuchen, kaufe ich Ihnen ein Bier.

Any Electron tips that might be useful to other developers?​

1. Benutzen Sie die Build-Werkzeuge, die dort draußen sind. Sie wollen nicht mit Ihren eigenen Lösungen ringen, vertrauen Sie mir. Benutzen Sie electron-builder. Verwenden Sie eine Boilerplatten-Repo.
2. If you need to open an issue in the Electron repo, go the extra mile to make it easy to reproduce. You'll get a response much more quickly, and the team will appreciate it. Even better, try fixing it yourself. It's actually pretty interesting to see the innards.
3. Read through all the guides and advanced docs at least once.
4. Don't build a browser, it's a saturated market.

The Electron community is growing quickly, and people are creating powerful new apps and tools at an astounding rate. To celebrate this creative momentum and keep the community informed of some of these new projects, we've decided to start a weekly blog series featuring noteworthy Electron-related projects.

This post is the first in the series, and features Kap, an open-source screen recording app built by Wulkano, a geodistributed team of freelance designers and developers.

What is Kap?​

Kap is an open-source screen recorder built primarily for designers and developers to easily capture their work. People use it to share animated prototypes, document bugs, create silly GIFs and everything in-between.

We have seen people of all age and backgrounds use it in educational settings, screencasts, tutorials... die Liste geht weiter. Even to create production assets! We're completely blown away by how well received our little side project has been.

Why did you build it?​

That's a very good question, it's not like there's a lack of screen recorders out there! We felt the alternatives were either too complex, too expensive or too limited. Nothing felt just right for our everyday needs. We also think it's great when the tools we use to do our work are open-source, that way everyone can help shape them. Building Kap ended up being just as much about what we didn't do. It's all in the details, an accumulation of small improvements that became the outline of a tool we wanted to use.

However, and maybe most importantly, Kap has become a place for us to leave our worries at the door and just have fun building something for ourselves and people like us. It's so important to create an environment where you get to just vent, try new thins and enjoy your craft. No requirements, no pressure, no expectations. Should designers and developers side project? Why, yes. Yes, they should.

Why did you choose to build Kap on Electron?​

There were a number of reasons:

• Web tech
• Most of the team are web developers
• We're invested in JavaScript
• It opens the door for more people to contribute
• Electron itself is open-source
• The power and easily maintainable modularity of node_modules
• Cross-platform possibilities

We think the future of apps are in the browser, but we're not quite there yet. Electron is an important step in the journey towards that future. It not only makes the apps themselves more accessible, but also the code they're built with. An interesting thought is imagining a future where the OS is a browser, and the tabs are essentially Electron apps.

Additionally, being primarily web developers, we're big fans of the isomorphic nature of JavaScript, in that you can run JS on the client, server, and now the desktop. With web tech (HTML, CSS and JS), many things are much simpler than native: Faster prototyping, less code, flexbox > auto-layout (macOS/iOS).

What are some challenges you've faced while building Kap?​

Using the resources Electron has available to record the screen was the biggest challenge. They simply weren't performant enough to meet our requirements and would render the project a failure in our eyes. Though at no fault of Electron itself, there's still a gap between native development and building desktop apps with web tech.

We spent a lot of time trying to work around the poor performance of the getUserMedia API, an issue originating in Chromium. One of our main goals when we set out to make Kap was to build the entire app with web tech. After trying everything we could to get it working (the minimum requirement being 30 FPS on a Retina screen), we eventually had to find another solution.

I see some Swift code in the repo. What's that about?​

Being forced to look for alternatives to getUserMedia, we started experimenting with ffmpeg. Besides being one of the best tools for audio and video conversion it has the functionality of recording the screen in almost any OS, and we were able to record crispy video meeting our minimum requirement of 30 FPS on a Retina screen. Problem? The performance was "😩", the CPU usage was going haywire. So we went back to the drawing board, discussed our options and realised that we had to make a compromise. That resulted in Aperture, our own screen recording library for macOS written in Swift.

In what areas should Electron be improved?​

We all know that Electron apps can have a thing for using RAM, but again, that's really a Chromium thing. It's part of how it works and it really depends on what you're running, for example Kap and Hyper typically use less than 100MB of memory.

One of the biggest areas of improvement that we see is payload, particularly how Electron distributes Chromium. One idea would be to have a shared Electron core and make app installers check if it's already present on the system.

Creating cross-platform Electron apps could be a better experience. Right now there are too many inconsistencies, platform-specific APIs, and missing features between platforms, making your codebase littered with if-else statements. For example, vibrancy is only supported on macOS, the auto-updater works differently on macOS and Windows, and is not even supported on Linux. Transparency is a hit or miss on Linux, usually miss.

It should also be easier to call native system APIs. Electron comes with a very good set of APIs, but sometimes you need functionality it doesn't provide. Creating a native Node.js addon is an option, but it's painful to work with. Ideally Electron would ship with a good FFI API, like fastcall. This would have enabled us to write the Swift part in JavaScript instead.

What are your favorite things about Electron?​

Our favorite thing is easily the fact that anyone with knowledge of creating for the web can build and contribute to multi-platform native experiences. Not to mention the ease and joy of developing on it, the excellent documentation and the thriving ecosystem.

From a front-end perspective, building Kap felt no different than building a simple website using browser APIs. Electron does a really great job of making app development similar (basically identical) to web development. So simple in fact that there was no need for frameworks or similar to help us, just clean and modular JS and CSS.

We are also huge fans of the team building it, their dedication and support, and the active and friendly community they maintain. Hugs to all of you!

What's coming next in Kap?​

The next step for us is to review the app in preparation for our 2.0.0 milestone, which includes a React re-write in addition to support for plugins, allowing developers to extend the functionality of Kap! We invite everyone to follow to project and contribute on our GitHub repository. We're listening and want to hear from as many of you as possible, let us know how we can make Kap the best possible tool it can be for you!

What is Wulkano?​

Wulkano is a design studio and digital collective, a team of remote technologists who love working together on both client gigs and our own projects. We're a distributed but tight knit group of people from different places and backgrounds, sharing knowledge, ideas, experiences, but most importantly silly GIFs and memes, in our virtual office (which happens to be the Electron based Slack!).

Any Electron tips that might be useful to other developers?​

Take advantage of and get involved in the fantastic community, check out Awesome Electron, look at examples and make use of the great docs!

We recently hosted an Electron hackathon at GitHub HQ for members of Hackbright Academy, a coding school for women founded in San Francisco. To help attendees get a head start on their projects, our own Kevin Sawicki created a few sample Electron applications.

If you're new to Electron development or haven't yet tried it out, these sample applications are a great place to start. They are small, easy to read, and the code is heavily commented to explain how everything works.

To get started, clone this repository:

git clone https://github.com/electron/simple-samples

To run any of the apps below, change into the app's directory, install dependencies, then start:

cd activity-monitor
npm install
npm start

Activity Monitor​

Shows a doughnut chart of the CPU system, user, and idle activity time.

Hash​

Shows the hash values of entered text using different algorithms.

Mirror​

Plays a video of the computer's camera at a maximized size like looking into a mirror. Includes an optional rainbow filter effect that uses CSS animations.

Prices​

Shows the current price of oil, gold, and silver using the Yahoo Finance API.

URL​

Loads a URL passed on the command line in a window.

Other Resources​

We hope these apps help you get started using Electron. Here are a handful other resources for learning more:

• electron-quick-start: A minimal Electron application boilerplate.
• Electron API Demos: An interactive app that demonstrates the core features of the Electron API
• electronjs.org/docs/all: All of the Electron documentation together on a single searchable page.
• hokein/electron-sample-apps: Another collection of sample applications for Electron, compiled by Electron maintainer Haojian Wu.
• awesome-electron - A GitHub repository that collects the latest and greatest Electron-related tutorials, books, videos, etc.

We've added a new userland section to the Electron website to help users discover the people, packages, and apps that make up our flourishing open-source ecosystem.

Origins of Userland​

Userland is where people in software communities come together to share tools and ideas. The term originated in the Unix community, where it referred to any program that ran outside of the kernel, but today it means something more. When people in today's Javascript community refer to userland, they're usually talking about the npm package registry. This is where the majority of experimentation and innovation happens, while Node and the JavaScript language (like the Unix kernel) retain a relatively small and stable set of core features.

Node and Electron​

Like Node, Electron has a small set of core APIs. These provide the basic features needed for developing multi-platform desktop applications. Diese Design-Philosophie ermöglicht es Electron, ein flexibles Werkzeug zu sein, ohne zu stark in der Art, wie es benutzt werden kann, einzuschränken.

Userland is the counterpart to "core", enabling users to create and share tools that extend Electron's functionality.

Collecting data​

To better understand the trends in our ecosystem, we analyzed metadata from 15,000 public GitHub repositories that depend on electron or electron-prebuilt

We used the GitHub API, the libraries.io API, and the npm registry to gather info about dependencies, development dependencies, dependents, package authors, repo contributors, download counts, fork counts, stargazer counts, etc.

We then used this data to generate the following reports:

• App Development Dependencies: Packages most often listed as devDependencies in Electron apps.
• GitHub Contributors: GitHub users who have contributed to numerous Electron-related GitHub repositories.
• Package Dependencies: Electron-related npm packages that are frequently depended on by other npm packages.
• Starred Apps: Electron apps (that are not npm packages) with numerous stargazers.
• Most Downloaded Packages: Electron-related npm packages that are downloaded a lot.
• App Dependencies: Packages most often listed as dependencies in Electron apps.
• Package Authors: The most prolific authors of Electron-related npm packages.

Filtering Results​

Reports like app dependencies and starred apps which list packages, apps, and repos have a text input that can be used to filter the results.

As you type into this input, the URL of the page is updated dynamically. This allows you to copy a URL representing a particular slice of userland data, then share it with others.

More to come​

This first set of reports is just the beginning. We will continue to collect data about how the community is building Electron, and will be adding new reports to the website.

All of the tools used to collect and display this data are open-source:

• electron/electronjs.org: The Electron website.
• electron/electron-userland-reports: Slices of data about packages, repos, and users in Electron userland.
• electron/repos-using-electron: All public repositories on GitHub that depend on electron or electron-prebuilt
• electron/electron-npm-packages: All npm packages that mention electron in their package.json file.

If you have ideas about how to improve these reports, please let us know opening an issue on the website repository or any of the above-mentioned repos.

Thanks to you, the Electron community, for making userland what it is today!

Elektron 1.4. 2 enthält einen wichtigen Patch, der ein Upstream Chrome Problem behebt, bei dem einige Symantec, GeoTrust, und Thawte SSL/TLS-Zertifikate werden 10 Wochen nach der Build-Zeit von libchromiumcontent, der zugrundeliegenden Chrome-Bibliothek von Electronic falsch abgelehnt. There are no issues with the certificates used on the affected sites and replacing these certificates will not help.

In Electron 1.4.0 — 1.4.11 HTTPS requests to sites using these affected certificates will fail with network errors after a certain date. This affects HTTPS requests made using Chrome's underlying networking APIs such as window.fetch, Ajax requests, Electron's net API, BrowserWindow.loadURL, webContents.loadURL, the src attribute on a <webview> tag, and others.

Upgrading your applications to 1.4.12 will prevent these request failures from occurring.

Note: This issue was introduced in Chrome 53 so Electron versions earlier than 1.4.0 are not affected.

Impact Dates​

Below is a table of each Electron 1.4 version and the date when requests to sites using these affected certificates will start to fail.

You can verify your app's impact date by setting your computer's clock ahead and then check to see if https://symbeta.symantec.com/welcome/ successfully loads from it.

More Information​

You can read more about this topic, the original issue, and the fix at the following places:

• What is Certificate Transparency?
• Symtantec knowledge base article
• Chrome issue 664177
• Chrome fix for issue 664177
• libchromiumcontent patch for issue 664177

Here are the new Electron apps and talks that were added to the site in September.

This site is updated with new apps and meetups through pull requests from the community. Sie können das Repository beobachten, um Benachrichtigungen über neue Erweiterungen zu erhalten oder wenn Sie nicht an allen der Änderungen der Seite interessiert sind, abonnieren Sie den Blog RSS-Feed.

Wenn Sie eine Electron-App erstellt haben oder ein Meeting veranstalten, erstellen Sie einen Pull-Request, um sie zur Seite hinzuzufügen und es wird die nächste Roundup.

New Talks​

In September, GitHub held its GitHub Universe conference billed as the event for people building the future of software. There were a couple of interesting Electron talks at the event.

• Making Electron Development Simpler, More Pleasant, and More Productive by Machisté Quintana, a Software Engineer at Slack.
• Electron: Desktop Apps with Web Languages by Zeke Sikelianos, an Electron Developer at GitHub.

Also, if you happen to be in Paris on December 5, Zeke will be giving an Electron talk at dotJS 2016.

Neue Apps​

	Pexels	Search for completely free photos and copy them into your clipboard
	Timestamp	A better macOS menu bar clock with a customizable date/time display and a calendar
	Harmony	Music player compatible with Spotify, Soundcloud, Play Music and your local files
	uPhone	WebRTC Desktop Phone
	SealTalk	Instant-messaging App powered by RongCloud IM Cloud Service and IM SDK
	Infinity	An easy way to make presentation
	Cycligent Git Tool	Straightforward, graphic GUI for your Git projects
	Foco	Stay focused and boost productivity with Foco
	Strawberry	Win Diners for Life Know and serve them better with the all-in-one restaurant software suite.
	Mixmax	See every action on your emails in real-time Compose anywhere.
	Firebase Admin	A Firebase data management tool
	ANote	A Simple Friendly Markdown Note
	Temps	A simple but smart menubar weather app
	Amium	A work collaboration product that brings conversation to your files
	Soube	Simple music player
	(Un)colored	Next generation desktop rich content editor that saves documents with themes HTML & Markdown compatible. For Windows, OS X & Linux.
	quickcalc	Menubar Calculator
	Forestpin Analytics	Financial data analytics tool for businesses
	Ling	REST Client
	Shortexts	Shortcuts for texts you copy frequently, folders and emojis
	Front-End Box	Set of front-end-code generators

Today we're announcing some improvements to Electron's documentation. Every new release now includes a JSON file that describes all of Electron's public APIs in detail. We created this file to enable developers to use Electron's API documentation in interesting new ways.

Schema overview​

Each API is an object with properties like name, description, type, etc. Classes such as BrowserWindow and Menu have additional properties describing their instance methods, instance properties, instance events, etc.

Here's an excerpt from the schema that describes the BrowserWindow class:

{
  Name: 'BrowserWindow',
  description: 'Browser-Fenster erstellen und steuern. ,
  Prozess: {
    main: true,
    renderer: false
  },
  Typ: 'Class',
  instanceName: 'win',
  slug: 'browser-window',
  websiteUrl: 'https://electronjs. rg/docs/api/browser-window',
  repoUrl: 'https://github.com/electron/electron/blob/v1.4.0/docs/api/browser-window. d',
  staticMethoden: [...],
  instanceMethoden: [...],
  Instanzeigenschaften: [...],
  Instanzereignisse: [...]
}
}

And here's an example of a method description, in this case the apis.BrowserWindow.instanceMethods.setMaximumSize instance method:

{
  name: 'setMaximumSize',
  signature: '(width, height)',
  description: 'Sets the maximum size of window to width and height.',
  parameters: [{
    name: 'width',
    type: 'Integer'
  }, {
    name: 'height',
    type: 'Integer'
  }]
}

Using the new data​

To make it easy for developers to use this structured data in their projects, we've created electron-docs-api, a small npm package that is published automatically whenever there's a new Electron release.

npm install electron-api-docs --save

For instant gratification, try out the module in your Node.js REPL:

npm i -g trymodule && trymodule electron-api-docs=apis

How the data is collected​

Electron's API documentation adheres to Electron Coding Style and the Electron Styleguide, so its content can be programmatically parsed.

The electron-docs-linter is a new development dependency of the electron/electron repository. It is a command-line tool that lints all the markdown files and enforces the rules of the styleguide. If errors are found, they are listed and the release process is halted. If the API docs are valid, the electron-json.api file is created and uploaded to GitHub as part of the Electron release.

Standard Javascript and Standard Markdown​

Earlier this year, Electron's codebase was updated to use the standard linter for all JavaScript. Standard's README sums up the reasoning behind this choice:

Adopting standard style means ranking the importance of code clarity and community conventions higher than personal style. This might not make sense for 100% of projects and development cultures, however open source can be a hostile place for newbies. Setting up clear, automated contributor expectations makes a project healthier.

We also recently created standard-markdown to verify that all the JavaScript code snippets in our documentation are valid and consistent with the style in the codebase itself.

Together these tools help us use continuous integration (CI) to automatically find errors in pull requests. This reduces the burden placed on humans doing code review, and gives us more confidence about the accuracy of our documentation.

A community effort​

Electron's documentation is constantly improving, and we have our awesome open-source community to thank for it. As of this writing, nearly 300 people have contributed to the docs.

We're excited to see what people do with this new structured data. Possible uses include:

• Improvements to https://electronjs.org/docs/
• A TypeScript definition file for more streamlined Electron development in projects using TypeScript.
• Searchable offline documentation for tools like Dash.app and devdocs.io

As a language with garbage collection, JavaScript frees users from managing resources manually. But because Electron hosts this environment, it has to be very careful avoiding both memory and resources leaks.

This post introduces the concept of weak references and how they are used to manage resources in Electron.

Weak references​

In JavaScript, whenever you assign an object to a variable, you are adding a reference to the object. As long as there is a reference to the object, it will always be kept in memory. Once all references to the object are gone, i.e. there are no longer variables storing the object, the JavaScript engine will recoup the memory on next garbage collection.

A weak reference is a reference to an object that allows you to get the object without effecting whether it will be garbage collected or not. You will also get notified when the object is garbage collected. It then becomes possible to manage resources with JavaScript.

Using the NativeImage class in Electron as an example, every time you call the nativeImage.create() API, a NativeImage instance is returned and it is storing the image data in C++. Once you are done with the instance and the JavaScript engine (V8) has garbage collected the object, code in C++ will be called to free the image data in memory, so there is no need for users manage this manually.

Ein weiteres Beispiel ist das Verschwindendes Problem, die visuell zeigt, wie das Fenster Müll gesammelt wird, wenn alle Referenzen auf ihn verschwunden sind.

Testing weak references in Electron​

There is no way to directly test weak references in raw JavaScript since the language doesn't have a way to assign weak references. The only API in JavaScript related to weak references is WeakMap, but since it only creates weak-reference keys, it is impossible to know when an object has been garbage collected.

In versions of Electron prior to v0.37.8, you can use the internal v8Util.setDestructor API to test weak references, which adds a weak reference to the passed object and calls the callback when the object is garbage collected:

// Code unten kann nur auf Electron < v0.37.8 ausgeführt werden.
var v8Util = process.atomBinding('v8_util');

var object = {};
v8Util.setDestructor(object, function () {
  console.log('The object is garbage collected');
});

// Remove all references to the object.
object = undefined;
// Manually starts a GC.
gc();
// Console prints "The object is garbage collected".

Note that you have to start Electron with the --js-flags="--expose_gc" command switch to expose the internal gc function.

The API was removed in later versions because V8 actually does not allow running JavaScript code in the destructor and in later versions doing so would cause random crashes.

Weak references in the remote module​

Apart from managing native resources with C++, Electron also needs weak references to manage JavaScript resources. An example is Electron's remote module, which is a Remote Procedure Call (RPC) module that allows using objects in the main process from renderer processes.

One key challenge with the remote module is to avoid memory leaks. When users acquire a remote object in the renderer process, the remote module must guarantee the object continues to live in the main process until the references in the renderer process are gone. Additionally, it also has to make sure the object can be garbage collected when there are no longer any reference to it in renderer processes.

For example, without proper implementation, following code would cause memory leaks quickly:

const { remote } = require('electron');

for (let i = 0; i < 10000; ++i) {
  remote.nativeImage.createEmpty();
}

The resource management in the remote module is simple. Whenever an object is requested, a message is sent to the main process and Electron will store the object in a map and assign an ID for it, then send the ID back to the renderer process. In the renderer process, the remote module will receive the ID and wrap it with a proxy object and when the proxy object is garbage collected, a message will be sent to the main process to free the object.

Using remote.require API as an example, a simplified implementation looks like this:

remote.require = function (name) {
  // Tell the main process to return the metadata of the module.
  const meta = ipcRenderer.sendSync('REQUIRE', name);
  // Create a proxy object.
  const object = metaToValue(meta);
  // Tell the main process to free the object when the proxy object is garbage
  // collected.
  v8Util.setDestructor(object, function () {
    ipcRenderer.send('FREE', meta.id);
  });
  return object;
};

Im Hauptprozess:

const map = {};
const id = 0;

ipcMain.on('REQUIRE', function (event, name) {
  const object = require(name);
  // Add a reference to the object.
  map[++id] = object;
  // Convert the object to metadata.
  event.returnValue = valueToMeta(id, object);
});

ipcMain.on('FREE', function (event, id) {
  delete map[id];
});

Maps with weak values​

With the previous simple implementation, every call in the remote module will return a new remote object from the main process, and each remote object represents a reference to the object in the main process.

The design itself is fine, but the problem is when there are multiple calls to receive the same object, multiple proxy objects will be created and for complicated objects this can add huge pressure on memory usage and garbage collection.

For example, the following code:

const { remote } = require('electron');

for (let i = 0; i < 10000; ++i) {
  remote.getCurrentWindow();
}

It first uses a lot of memory creating proxy objects and then occupies the CPU (Central Processing Unit) for garbage collecting them and sending IPC messages.

An obvious optimization is to cache the remote objects: when there is already a remote object with the same ID, the previous remote object will be returned instead of creating a new one.

This is not possible with the API in JavaScript core. Using the normal map to cache objects will prevent V8 from garbage collecting the objects, while the WeakMap class can only use objects as weak keys.

To solve this, a map type with values as weak references is added, which is perfect for caching objects with IDs. Now the remote.require looks like this:

const remoteObjectCache = v8Util.createIDWeakMap()

remote.require = function (name) {
  // Tell the main process to return the meta data of the module.
  ...
  if (remoteObjectCache.has(meta.id))
    return remoteObjectCache.get(meta.id)
  // Create a proxy object.
  ...
  remoteObjectCache.set(meta.id, object)
  return object
}

Note that the remoteObjectCache stores objects as weak references, so there is no need to delete the key when the object is garbage collected.

Native code​

For people interested in the C++ code of weak references in Electron, it can be found in following files:

The setDestructor API:

• object_life_monitor.cc
• object_life_monitor.h

The createIDWeakMap API:

• key_weak_map.h
• atom_api_key_weak_map.h

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