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Knockout

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A Julia wrapper for Knockout.js. It uses WebIO to load JavaScript and to do Julia to JS communication. Go here to get started with WebIO.

Usage

The package exports a single knockout function:

knockout(template, data; options...)

  • template acts as the "structre" of the UI. It's normal HTML, but can use variables from data. See the Knockout documentation for more details. You can compose the template (like any HTML) using WebIO.
  • data is an iterable of propertyName => value pairs (e.g. a Dict) which populates the template.
using Knockout, WebIO

template = node(:p, "{{message}}", attributes = Dict("data-bind" => "visible : visible"))
knockout(template, [:message=>"hello", :visible=>true])

If a property's value is an observable, this function syncs the property and the observable. Here's how you can update the properties bound to the template from Julia.

using Observables
ob = Observable("hello")
knockout(template, [:message=>ob, :visible=>true])

Now if at any time you run ob[] = "hey there!" on Julia, you should see the contents of the message update in the UI. Try making an observable for :visible property and set it to true or false, you should see the message toggle in and out of view!

To initiate JS to Julia communication you must set an event handler on scope[propertyName] (by calling on(f, scope[propertyName])) before rendering the scope.

Here's an example of JS to Julia communication:

incoming = Observable("")
on(println, incoming) # print to console on every update

template = node(:input, attributes = Dict("type"=>"text", "data-bind" => "value : message"))()
knockout(template, [:message=>incoming])

This will cause the value of the textbox to flow back to Julia, and should get printed to STDOUT since we have a listener to print it. The value only gets updated on change (meaning when the widget loses focus). To update it on input (meaning whenever the user interacts with the widget) use:

incoming = Observable("")
on(println, incoming) # print to console on every update

template = node(:input, attributes = Dict("type"=>"text", "data-bind" => "value : message, valueUpdate : 'input'"))()
knockout(template, [:message=>incoming])

You can specify that you want some knockout observable to be computed as a function of other observables, e.g knockout(...; computed = Dict(:fullName => @js function(){this.firstName() + ' ' + this.lastName()})). You can pass functions that you want available in the Knockout scope as keyword arguments to knockout E.g. knockout(...; methods=Dict(:sayhello=>@js function(){ alert("hello!") })) (Tip: use JSExpr.jl for the @js macro)

Acknowledgments

This package is strongly inspired by Vue.jl. It basically is a word by word translation of Vue.jl for Knockout.js. Knockout.js solves one major technical difficulty of Vue.js: the impossibility of nesting instances.