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Knockout 3.2.0 released

This one has been slow-cooking since February and it’s good. For the first time in a while, this release focuses on adding some significant new features to Knockout. Almost any developer using KO should seriously consider making use of these, as they can greatly streamline your code.

So what’s new?


Components bring a new and hugely more scalable way of structuring a large application. They:

  • Combine a viewmodel and template in an encapsulated package
  • Can represent either small reusable widgets or entire sections/pages in a larger app
  • Can be preloaded, or loaded on demand
  • Can be nested or inherited
  • Can work with custom conventions for configuration or loading.

I’ve built a few apps with KO components recently (including the KO triage site, and an iOS/Android game called Blockpick (not open source)) and can confidently say this is how I’ll be structuring my KO apps from now on.

See: components overview documentation and explore from there. Or if you’re in the mood to get a hot drink and settle in for a demo, see this video from NDC Oslo 2014.

Custom elements

Custom elements provide many of the benefits of the emerging Web Components spec, but cleanly integrated with KO’s new components feature described above. Plus, they’re ready to use in production today – compatible all the way back to IE6!

See: custom elements documentation

Pure computeds

ko.computed has always been the powerhouse behind KO, underpinning just about all of its features. It makes your code reactive without you having to declare any dependencies explicitly.

ko.pureComputed is a new specialisation of ko.computed with better performance and memory management in many cases. It automatically pauses/resumes evalution, and automatically releases/reclaims references to dependencies, according to whether any other part of your app is watching it at the time. This can be extremely valuable for large single-page applications, where you may be tearing down and rebuilding different parts of your UI over long periods of time, and need to ensure your memory/CPU use is as streamlined as possible.

See: pure computed documentation

The textInput binding

This new binding transparently resolves numerious browser event quirks related to text entry. You might not believe how many different types of events are raised (or worse: not raised) by different browsers when a user types, cuts, pastes, drags, or autocompletes text in an <input> or <textarea>. Or if you’ve been a web developer for a while, you probably would believe it, and have the battle scars to show.

Well, textInput is something of an expert on the subject, so hopefully you don’t have to be.

See: textInput documentation


Of course, there are smaller bugfixes in there too. You can find the exact set of changes on GitHub.

Hopefully these enhancements will prove valuable for your projects. I’ve been using most of them for a while and have certainly found them useful. Big thanks to everyone who’s participated in implementing and discussing these changes!

52 Responses to Knockout 3.2.0 released

  1. Kim Tranjan

    Amazing! You guys are awesome, thank you very much.

  2. Thanks Steve! This is the best KO ever.

  3. Igor Blinnikov

    Hi, Steve.

    With introducing the new observable type “pureComputed” do we still need the old “computed” counterpart? What is the difference between them except performance? When should I use pureComputed and when just computed?


  4. Daniel

    Hmm… for some reason, cloning from only retrieves the “deploy” branch.
    Is that on purpose?

  5. Daniel

    I switched to “master” branch and I got the entire repository.

  6. Kudos to the entire team! It’s great to see you guys are still improving KO in a sensible way and are so focused on browser compat.

  7. Puneet

    Fantastic to find that Knockout still evolving. It must still be the best performing JavaScript MVVM lib out there.

    Checked out master branch of, switched to master. But npm install is giving errors while installing some components like graceful-fs. Do I need to run a particular version of node? I am running 0.11.13

  8. Fredrik

    Great news! Looking forward to trying out directives.

    By the way, I’ve just started using Angular on a big project after having used Knockout on a previous one. And I find that Knockout really does fill another space than Angular, really liking KO’s expressiveness.

  9. HMR

    This is awesome. I’m excited to use the new features. When will the nuget package be updated to 3.2?

  10. Excellent. I am a fan of web components and its great that knockout.js is jumping on the wagon. It is unfortunate that knockout.js is not getting its due press-time compared to Angular.js (bloated- all things to eveyone) and Ember.js (Ogre-like where you have to do in a certain way or else the world will implode)

  11. Great work guys. I am gonna use new features soon.

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  13. Mike

    Good job!
    Any breaking changes to the prev. version?

  14. Lucas

    Hey man, great work on knockout 3.2.0, very cool the components feature, a lot of stuff can be done with that, already using it since beta :D

    A quick question: whats the stack you are using in your game? I ve been searching a lot ways to develop mobile applications using html5/phonegap, but all those frameworks dont seem to fit nice with knockout.

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  19. Baljeet Sandhu

    This is great! KO is the best combo of power and simplicity.

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  21. Justin

    A nice release, but this doesn’t appear to use or support real W3C custom elements.

    Are there any plans to produce real custom elements from Knockout components?

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  27. Congratulations and thanks for version 3.2 of Knockout. The KO Components feature is just a great addition to Knockout. This one feature that will make web app development with Knockout so much more streamlined.

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  30. stickyfeet

    Knockout was great, now it’s sublime! Using Knockout components / custom elements, I was able to finally come up with a really elegant solution for sticky page footers:

    Great work! :)

  31. Born2code

    I have the same question as Lucas. I know blockpick is not open source but can you advice on the choice of stack? did you use phonegap?
    much appreciated (and all the other awesome work on knockout, we use it extensively)

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