UnderscoreKO - Want some lumps of Underscore.js sugar in your Knockout java?

Published on Tuesday, March 13, 2012

I've been using Knockout at work for a MVC3 project and I have also been using Backbone.js in some personal projects at home. I really love Underscore and the array manipulation it offers for Node and the browser. I also liked how it was integrated into Backbone collections.

Yesterday evening as I drove home from work, I had a crazy idea. An idea so simple, I was really surprised only one other person (that a 1 second Google search turned up) made an attempt to do. Maybe because it's so simple, no one bothered to make their code public.

Can you guess what my idea was? C'mon, isn't it obvious? Why not marry Underscore's array methods to Knockout's observable arrays? And BAM, in one evening, a tiny library named UnderscoreKO was born. It's really very cute. It took me maybe 20 minutes to write the library and then 3 hours to write the tests and package it up. Go figure.

Get UnderscoreKO

You can download the UnderscoreKO package off of Nuget, since I know that's how a lot of you roll.

The source is also available on GitHub.

Let's see some code

First, let's see what life was like before UKO:

vm.computedArray = ko.computed(function () {
    // marry the two arrays
    return _.union(this.someArray(), [0, 1, 2, 3, 4]);
}, vm);

So what problem have I "solved"? A small one, but I hope small enough that you'll miss it when you can't do it (those are the best, right?):

vm.computedArray = ko.computed(function () {
    // marry the two arrays
    return this.someArray.union([0, 1, 2, 3, 4]);
}, vm);

Do you see it? Here, let me zoom in:

return this.someArray.union([0, 1, 2, 3, 4]);

That's right! All of Underscore's array and collection methods are now available off of observable arrays! You didn't even know you wanted this, right?


thelinuxlich had a neat feature in her plugin which was the idea of "destructive" methods that were basically convenience methods to manipulate the observable array directly.

In other words, this:

vm.myObservableArray(vm.myObservableArray.union([0, 1, 2, 3]));

Becomes this:

vm.myObservableArray.union_([0, 1, 2, 3]);

See? Isn't that a little nicer? I added "mutator" methods (methodName_) for anything I felt you'd want to use to manipulate the array. And of course, they still use Knockout underneath so change notifications still occur.


Um... what you'd expect? Actually, there are a couple issues I'd like to address tonight in another update (such as adding chain which I forgot about and taking care of passing in observableArrays to some functions like union so you don't have to do this: vm.myObservableArray.union_(vm.array1(), vm.array2(), ...)). I've released v1.1 which fixes a mutator bug, adds chain() support, and invokes KO arrays when passed to certain functions like union.

Live Demo

Want to try before you buy? Go ahead!

About Kamran
I'm a technologist, speaker, and Pluralsight author and I specialize in building full-stack solutions with a focus on modern web technology and cloud native architecture.
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