Knockout 3.5.0 beta release notes
Full list of issues: https://github.com/knockout/knockout/milestone/9?closed=1
Important: This release includes some minor breaking changes to the foreach
binding to improve performance and clarify features. These changes can be turned off using global options.
When using the
as
option with theforeach
binding, Knockout will set the named value for each item in the array but won't create a child context. In other words, when usingas
, you will have to use the named value in bindings:text: item.property
rather thantext: property
. This can be controlled by settingko.options.createChildContextWithAs = true
. (See #907)To improve performance when array changes are from a known, single operation, such as
push
, theforeach
binding no longer filters out destroyed items by default. To turn this off and filter out destroyed items, you can setincludeDestroyed: false
in theforeach
binding or setko.options.foreachHidesDestroyed = true
to use the previous behavior by default. (See #2324)
Other enhancements
- You can react to the completion of bindings such as
if
andwith
using the newchildrenComplete
binding or subscribing to thechildrenComplete
binding event.
(See #2310) - You can react to the completion of components, including nested components, by including a
koDescendantsComplete
method in the component viewmodel or subscribing to thedescendantsComplete
binding event. (See #2319) - Binding strings can include template literals (backticks) and C++ and C-style comments.
- Observable arrays include
sorted
andreversed
methods that return a modified copy of the array. This is in contrast tosort
andreverse
that modify the array itself. - The new
class
binding supports dynamic class strings. This allows you to use thecss
andclass
bindings together to support both methods of setting CSS classes. - The new
using
binding, similarly towith
, binds its descendant elements in the context of the child viewmodel. Unlikewith
, which re-renders its contents when the viewmodel changes,using
will just trigger each descendant binding to update. - The new
hidden
binding works oppositely tovisible
. - The new
let
binding allows you to set values that can be used in all descendant element bindings, regardless of context. - Similarly to
let
, you can set such values at the root context by providing a function as the third parameter toko.applyBindings
. (See #2024) - Performance improvement: String templates are no longer parsed each time they are referenced. Instead the parsed nodes are cached and cloned.
- Observables notify a new
spectate
event whenever their value changes. Unlike the standardchange
event, this new event isn't necessarily delayed by rate-limiting or deferred updates. You can subscribe to the event without waking a sleeping pure computed; the computed will notify the event if it is accessed with a new value. - Computed observables include a
getDependencies
method that returns an array of the observables that the computed is currently watching. - The
attr
binding supports namespaced attributes such asxlink:href
insvg
elements. - The
ko.when
function allows you to run code once when an observable or condition becomes true. - The
ko.isObservableArray
function can be used to check if something is ako.observableArray
. - The
style
binding will usejQuery
if present. Even without jQuery, the binding now supports standard style names, such asbackground-color
, and automatically appendspx
if needed to styles that expect it. - Knockout will throw an error if it finds an unmatched closing virtual element (
<!--/ko-->
).
Fixes
30 or so separate fixes are included in this release,
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New to all this? Now’s a great time to check it out. Fsx product key. Knockout is an MVVM library for JavaScript – it makes rich dynamic web UIs easier and cleaner to build. The best place to start learning is with the interactive tutorials.
What just happened?
- The finished 2.0.0 build is now on GitHub
- All of the documentation and live examples are updated to reflect the new version
- All of the interactive tutorials are updated too.
Credits go to the many community members who contributed pull requests, bug reports, new documentation, and support during this process. These people include aaronpowell, amonat, antis, aredridel, artiomchi, barkmadley, b-dur, bmac, cburgdorf, develop-me, DomenicDenicola, doodlemoonch, dre2901, drewlesueur, ducka, gigi81, GLuKKi, hunterloftis, ifandelse, joeldart, kmalakoff, lcbarcellos, mbest, mtscout6, neonstalwart, owenssam, Quaternion, rniemeyer, RoyJacobs, schinckel, seanami, SimonBartlett, studgeek, tehsenaus, and tiberiuana – and that’s just those who made recent pull requests (apologies for not tracking everyone who contributed other things). rniemeyer wrote a lot of documentation too.
Why is it called 2.0.0? Why not 1.3.0?
For a long time, we were planning this next version to be called 1.3.0. However,
- Quite a few community members are keen on adopting SemVer-style versioning. 2.0.0 is a good place to start (expermentally) with that versioning convention.
- It’s such a big set of core changes that if this doesn’t count as 2.0, I guess nothing ever would…
New features
I’m mostly going to copy and paste the “what’s new” list from my earlier blog post about Knockout 1.3 beta, with a few further updates. Besides these things, there are all the usual bugfixes and performance improvements that you’d expect.
1. Control flow bindings
Previously, if you wanted to display a repeating sequence of UI elements (“foreach”), or have a section of the DOM exist only if some viewmodel condition was true (“if”), you’d need to create an entire template to define that. A bit cumbersome for something so simple and commonplace! Now you can use the new control flow bindings – if, ifnot, with, and foreach – to achieve basic, declarative control flow without the need for a template. This can make your code a lot more elegant and to-the-point.
Here’s an example of using “foreach” and “if”:
Tip: Switch to the “result” tab to see the output
The “with” binding changes the binding context to whatever object you specify. This makes it easy to compose many independent view models together – you have a host model that contains references to its children, and then use “with” to bind different sections of the page to different child models. Example:
Of course, the “if”, “ifnot”, “foreach”, and “with” bindings can all be combined and nested arbitrarily.
2. Containerless control flow
What if you want to set up template-less control flow (as in the above example), but without having to use extra container elements just to hold the “foreach”, “if”, etc., bindings? In that case, you can use the new comment-based control flow syntax like this:
The comment-based control flow syntax works with the “if”, “ifnot”, “foreach”, “with”, and “template” bindings. In a large number of cases, this means you can skip string-based templates and use the binding-based control flows instead, which can run much faster depending on what exactly you’re doing.
3. Access to parent binding contexts
Whether you’re using regular nested templates, or nesting the new control flow blocks, sometimes you want to reference properties that exist at the upper levels of binding. There are four new pseudo-variables that you can use in any binding (inside or outside traditional templates):
- $data – returns the current item
- $parent – returns the item from the parent binding context
- $parents – an array containing all the parent binding contexts. $parents[0] $parent, then $parents[1] is the level above that, and so on.
- $root – returns the item at the top level of binding (usually your primary view model)
Example:
Knockout 2.0
4. Cleaner event handling
In most cases,>Note:ko.computed is Knockout 2.0’s new name for ko.dependentObservable – it’s easier to say, type, and explain. This doesn’t affect backward compatibility, though – ko.dependentObservable still works, because it references the same function instance as ko.computed at runtime. You don’t have to change your existing code if you don’t want.
Occasionally, it’s desirable to limit how fast observables and computed observables update. For example, you might be using a ko.computed to invoke Ajax requests whenever a set of observables change. Sometimes you might want to change multiple underlying observables, but only have that ko.computed re-evaluate once, after all the changes (so that it only fires one Ajax request). Effectively, you want a kind of atomic update.
This is now pretty easy to do: you can apply an extender called “throttle” either to observables or to computed observables. For example:
The way this works is that, when throttled, notifications and evaluations are done asynchronously, and don’t occur at all until they stop being triggered for the specified throttle timeout duration.
In the case of making a computed value only update once even if there are multiple synchronous changes to its dependencies, you can use a very short timeout (for example, 1ms), and then it will re-evaluate as soon as possible after any series of synchronous changes to its dependencies. Example:
Breaking changes
There are two changes that might realistically affect existing 1.2.x application code. Both are for good reasons and are important for the long-term health of the project…
- Event handlers now receive your model object as their first parameter, and the DOM event object as the second parameter. Previously, they only received the DOM event object as the first parameter. So, if you are using the “click” or “event” bindings and are specifically catching and using the DOM event object, you’ll need to change your handler’s signature from this:
myViewModel.myEventHandler = function(evt) { /* do something with evt */ }
… to this: Acrimony movie download mp4.
myViewModel.myEventHandler = function(data, evt) { /* do something with evt */ }
This will not affect any event handlers that don’t specifically receive and process the “event” parameter. We chose to make this change because it significantly simplifies event handling in the majority of cases. Most developers have been able to upgrade to 2.0.0 beta without changing their applications at all.
- KO 2.0.0 drops support for very old versions of jquery-tmpl. If you need to use string-based templating (and most often you won’t now that KO 2.0.0 has native control flow bindings), get jquery-tmpl 1.0.0pre. But also consider dropping the string-based templating, and switching to control flow bindings instead, as jquery-tmpl is no longer in active development.
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Summary
![2.0 2.0](https://s3.sbodypak.pl/img/p/1/0/0/7/6/10076-thickbox_default.jpg)
Try the updated interactive tutorials, update your existing KO applications, have a great Christmas/vacation/newyear
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Let's start with a thanks in advance :)
OK, So I'm trying to load/map hierarchical TypeScript/KnockoutJS typed classes from matching JSON data using the knockout.mapping plugin, the hierarchy can be to the Nth degree.
I know I can do the following to map/load the top level class from the JSON data.
However I can't figure out is how to map/load complex, Nth degree, hierarchical JSON data to a set of TypeScript/KnockoutJS classes and build the parent/child relationship.
I've read countless articals, but they all fall short when it comes to hierarchical relationships beyond simple parent/child examples, and I can find none using the knockout.mapping plugin.
Here are my cut down definitions of TypeScript classes I wish to map/load. I'm a c++/c# developer, so JavaScript of this nature is very new to me.
TypeScript Objects
The JSON would look something like this:
2 Answers
OK, so I'm a little further down the line now, after lots of hair pulling and numerious tests.
Below is a almost working example of what I'm trying to achive, the only problem with this is it doesn't seem to map correctly, even though stepping through the code seems to suggest it is loading correctly. Only when I use it with my bindings it throws a null unreferenced binding on RootTaget.Filter.Type, which should have be populated with a value.
I'm still trying to figure out why, but I will welcome suggestions as to what possible wrong. :)
NOW FIXED AND WORKING
semi-working typescript
![Olimp knockout 2.0 Olimp knockout 2.0](https://www.picclickimg.com/d/l400/pict/153035169551_/OLIMP-KNOCKOUT-20-Pre-Workout-Stack-Muscle-Pump.jpg)
html binding test
Another approach is to create a .d.ts file that defines TypeScript interfaces that describe the nested collections of observable types that are generated by the knockout mapping plugin given your C# classes.
Then you get the type-checking you desire using the .d.ts file (the same way you would use a .d.ts file from the definitely typed github project to get type checking for existing javaScript libraries).
I created a console app to examine my c# dll using reflection. I used a custom attribute to mark the types for which TypeScript interfaces were to be created. (I had to also create a custom attribute to mark which properties were NOT to be created as observable, since the mapping plugin only makes the leaf nodes of your nested collections as observables).
This worked well for me as I was able to regenerate the .d.ts file quickly when my C# model changed. And I was able to have type-checking for all parts of my knockout ViewModel.