controller for knockout.js custom element - javascript

Sometimes a component/custom element has some UI logic which requires some UI code, it's something which can't be done by binding to the component's view-model.
For example, let's say the component needs to change the way it looks based on available space, and this requires manipulating elements by JavaScript code.
What I need is a controller for the UI.
For example, imagine we have a component called myGadget for which I have myGadget.html, myGadgetViewModel.js and I also want to have myGadgetView.js
Within the myGadgetView.js I want to have something like this:
function myGadgetView(element)
{
// element is the custom element's node
}
What is the best way to do this in Knockout?
Should I combine component with custom binding?
With a custom binding I could get access to the element, so the HTML of the component would look like this:
<script id="myBar-template">
<div data-bind="myGadget : ...">
</div>
</script>
and I need to put somewhere this:
ko.bindingHandlers.myGadget = {
init: function (element, valueAccessor)
{
// I have access to element node
var myGadgetView = new myGadgetView(element);
},
update: function (element, valueAccessor)
{
// I have access to element node
}
}
I'm not sure about using custom binding for this, I wonder if there's a better approach.
For example, I'm looking to the custom component loading, but I don't have a clear idea yet.

When defining a component, you can specify a createViewModel function. This function will be passed the element the component will be bound to. According the Knockout documentation, it's still preferable to use custom bindings to manipulate the view.

Any manipulation of the view should be done in binding handlers, but that doesn't mean you can't make something like a jQuery plug-in, which your myGadgetView.js would be, and use that in the binding handler. You just wouldn't want your plug-in to be aware of your viewmodel, nor your viewmodel to be aware of the plug-in. The binding handler would mediate, mapping viewmodel elements to plug-in parameters.

Related

Add HTML object to an event javascript/meteor

How can I add HTML objects to an event?I would like to do something like this:
Template.Schedule.events({
'dblclick .mycol' (event){
event.target.childNodes.append("<strong>Test</strong>");
}
});
I know I could style it and change the innerHTML and so on for the given example, but I actually want to add other HTML objects, like a select-tag, how can I do that?
The vanilla JS way
You could use innerHTML here to change the html content of the clicked element:
'dblclick .mycol' (event){
const target = event.currentTarget
target.innerHTML = target.innerHTML + "<strong>Test</strong>"
}
If you want to manipulate the parent in the event you can use outerHTML
The jQuery way
Your approach of using append is requiring jQuery:
'dblclick .mycol' (event){
$(event.currentTarget).append($("<strong>Test</strong>"))
}
Bonus: Optimization for using jQuery
In a meteor blaze template-events each event has a reference to the template instance. This template instance keeps a reference to a jQuery object and it's part of the DOM that it manipulates.
template.$ returns a jQuery object of those same elements. jQuery
objects are similar to arrays, with additional methods defined by the
jQuery library.
The template instance serves as the document root for the selector.
Only elements inside the template and its sub-templates can match
parts of the selector.
You can access it via templateInstance.$ if your seconds event parameter is namend templateInstance. With
'dblclick .mycol' (event, templateInstance){
templateInstance.$(event.currentTarget).append($("<strong>Test</strong>"))
}
This saves jQuery the need to traverse the whole DOM, makes it more efficient on large documents.
The Meteor Blaze way
Now these are neat little tricks when there is need for manipulation on a small scale. However, you may want your app to be scalable and profit all the time from the Blaze rendering engine.
In such cases you may rather want to generate a way of dynamically inserting templates.
Consider the following template, that is nowhere imported yet:
rowcontent.html
<template name="rowcontent">
<strong>Test</strong>
<p>someData{{someData}}</p>
</template>
rowcontent.js
import './rowcontent.html' // currently just the import
You can dynamically add it at runtime to an element using Blaze.renderWithData so:
'dblclick .mycol' (event, templateInstance) {
import './rowcontent.js' // use the right path here
Blaze.renderWithData(Template.rowcontent, {someData: 'toBePassedToRowContent'}, event.currentTarget)
}
which will result in:
This is my col Test
someDatatoBePassedToRowContent
The advantage of this approach is that you can pass the data to the template and have all the reactive benefits remaining, thus handle the newly added template like any other template in Meteor.
Alternatives
Declarative dynamic templates using Template.dynamic

Knockout "with" binding removes my jquery DOM events

I have several jquery dom events that are created on DOM load or document ready. These are mostly default behaviors that should be applied to all forms in my application. Example:
$('input:text').focus(function ()
{
$(this).select();
});
Right before applying knockout binding, I can check my dom elements and all events are there:
But when I run the applyBindings method to bind the viewmodel to my DOM, the "with" binding removes all events that are not related to knockout:
I have tried overwriting the cleanExternalData as explained on the documentation and on this answer. But that did not help with this, the function is replaced, but the events are still removed from the DOM when the templating is applied on the binding process.
For the record, this is not an exclusive behavior of the with function, but all anonymous templating functions also do that, foreach, if, ifnot. Using template, as expected, also behaves the same way. The DOM element is completely destroyed, stored as a template, then added again on my document when the condition is satisfied, but now without any jquery event handlers.
How to avoid that knockout removes the events from my DOM elements?
Instead of binding elements to a specific node, you can use a databinding to use the jquery on() functionality to handle events. Here's a binding I use:
define(['knockout'], function (ko) {
ko.bindingHandlers.eventListener = {
init: function (element, valueAccessor, allBindings, viewModel, bindingContext) {
var params = ko.utils.unwrapObservable(valueAccessor());
if (!(params instanceof Array)) {
params = [params];
}
params.forEach(function (param) {
$(element).on(param.event, param.selector, function (event) {
param.callback(ko.dataFor(this), ko.contextFor(this), event);
});
});
}
}
});
Usage:
<div data-bind="eventListener: [
{ event: 'click', selector: '.copyInclusionRule', callback: copyInclusionRule},
{ event: 'click', selector: '.deleteInclusionRule', callback: deleteInclusionRule}]">
... other knockout template stuff here ...
</div>
The above will listen for click events on either an element with the specified class and perform the callback when the event is received for anything within the div's 'scope'. The value of 'event' param can be anything that on() uses.
I think the reason why you can't leverage the cleanNode overrides is that your dom is being completely destroyed and re-created..at least that's my theory, if there was a way to get some kind of memory ID of the pre-applyBindings() dom elements and then after the applyBindings is called, are those new nodes? If they are new nodes, it's not something you can't fix with cleaning, those nodes are gone.
Alright, here is how I fixed my problem and I hope this can clarify things to others that don't want to destroy their DOM as well. If you don't want that knockout to destroy your DOM, that is possible since version 2.2. And thus, destroying the DOM when that is not necessary is not intended behavior and can be avoided.
I had tried several bidings created by Michael Best before, like his using binding that will come in knockout 3.5, and let or withLight (which became using now). None really worked. These simplified bidings would load the initial object, but not update the dom when this object properties had changed.
But this helped me to figure out what I am doing wrong. When I wanted to update my observable object, I was using myViewModel.observableObject(NewObject), like the documentation told me to do:
To write a new value to the observable, call the observable and pass the new value as a parameter. For example, calling myViewModel.personName('Mary') will change the name value to 'Mary'.
But I wasn't passing a single property's value, I was passing a new object that had the same structure (same properties). And this triggered knockout that the old object was destroyed (and thus, falsy for a second) and a new object took its place, even though all properties are there, they just got different values. Unlike the documentation told me, it didn't simply changed the value, but changed the entire object.
To go around this, instead of doing that, First, I had to initiate my viewModel with this object already created, using dummy data, this makes knockout not destroy the DOM when applyBindings is called. Then, when I want my object to update, I replaced the value of each property of the observable object to have the value of the new object. This didn't destroy the object and knockout updated my binding properly.
myViewModel.setSelectedItem = function setSelectedItem (newObject)
{
for (var prop in myViewModel.myObservableObject())
myViewModel.myObservableObject()[prop](newObject[prop]);
}
The with binding still killed some of my events (my angular ng-change for one of my components, for instance), but it kept all jquery events in there (which is great). And the using binding didn't kill any of my events at all (which is even better).

KnockoutJs Components - add default class

Knockout gives you two ways of instantiating a component, either with a custom html element or with the component binding.
However I have discovered a slight issue when trying to style the root component element. It's fine if you just use the custom element syntax as you can just assign css styles to that - however, if you then use the component binding, the css rules don't match and so they fail.
Ideally I want to support both scenarios as they both have their uses. If I could get knockout to add a class to the root component element which is just the component name it would solve the issue but reading the documentation it isn't clear where it would be best to do this.
I've already got a custom template loader which retrieves the template from an ajax call, but this template is just the inner html of the root node.
Basically I want this:
<my-custom-element>
...
...
<my-custom-element>
To become this:
<my-custom-element class="my-custom-element">
...
...
<my-custom-element>
Anyone got any ideas?
You can use "createViewModel" method and access element in the component (e.g. to add some class):
ko.components.register('some-component', {
viewModel: {
createViewModel: function(params, componentInfo) {
var $element = $(componentInfo.element.children[0]);
// some other code ...
}
},
template: "<div></div>"
});

How to use jQuery in a Knockout.js Template?

I'm trying to target an element using jQuery which is embedded in one of my knockout templates:
<script type="text/html" id="video-file-template">
<div class="video" data-bind="attr: { 'data-index': $index }">
</div>
</script>
Yet, when I attempt to select $('.video') using jQuery, wrapped in a document ready function, I get an object with a length of 0 returned:
$(document).ready(function() {
console.log($('.video')); // Returns an object with a length of 0
});
Why is this? Is it because the element is not part of the DOM when my jQuery script is evaluated? If so, how can I target the element when it is loaded into the DOM via Knockout.js?
It's true that the document is ready before ko.applyBindings finishes, so that's why you're not seeing the element. However, you should not be using jQuery to violate the boundary between your view model and the DOM like that. In knockout, the way to accomplish what you need is with custom bindings.
Basically, you define a new knockout binding (like text, value, foreach, etc) and you have access to an init function, which fires when the element is first rendered, and an update function, which fires when the value you pass to the binding is updated. In your case, you would only need to define init:
ko.bindingHandlers.customVideo = {
init: function (element) {
console.log(element, $(element)); // notice you can use jquery here
}
};
And then you use the binding like this:
<div data-bind="customVideo"></div>
Perhaps it's better to add the "video" class and do other initialization right in the init callback:
ko.bindingHandlers.customVideo = {
init: function (element) {
$(element).addClass('video');
}
};
If this feels a little wonky at first, remember there's a very good reason for the indirection. It keeps your view model separate from the DOM it applies to. So you can change the DOM more freely and you can test the view model more independently. If you waited for ko.applyBindings to finish and called some jQuery stuff after that, you'd have a harder time testing that code. Notice that knockout custom bindings are not "special" in any way, and you can see that the built in bindings are defined exactly the same: https://github.com/knockout/knockout/tree/master/src/binding/defaultBindings
As the previous comments have suggested, it's because your $(document).ready fires before your knockout templates have been rendered.
Whenever I need to do this sort of thing I tend to have an 'init' (or whatever) function on my ko view model that I call after applyBindings has completed;
So:
var ViewModel = function(){
var self=this;
//blah
self.init = function(){
//jquery targeting template elements
}
}
var vm = new ViewModel();
ko.applyBindings(vm);
vm.init();

How do I force knockout to rebind a custom binding?

I would like to know how I can force a knockout binding to refresh it's value. Normally we use an observable and that way the binding can happen automatically when the observable changes. But in my case I have created a custom binding:
if (!ko.bindingHandlers.asyncHtml) {
ko.bindingHandlers.asyncHtml = {
init: function (element, valueAccessor) {
var value = ko.utils.unwrapObservable(valueAccessor());
var parameters = value.params.concat([function (data) {
$(element).html(data);
} ]);
parameters.concat([function (data) {
$(element).html('Unable to retrieve html.');
} ]);
value.source.apply(null, parameters);
}
}
}
This is so that a function which performs an asynchronous JSON call can update the respective element (with the returned HTML) once the call completes. The element, a DIV in this case, looks like this:
<div id="myDiv" data-bind="asyncHtml: {source: getHtml, params: [myId()]}">
My problem is that, another feature on this page can change database values that require myDiv to be updated as a result. I can probably find a complicated way to correct this problem but I was wondering if there was a simpler way where I can just force the binding to reapply?
NOTE: getHtml is a function on my viewmodel which performs the JSON call to retrieve the HTML.
Thanks
I hope I understood what you are trying to accomplish correctly, but I am not sure, so let me explain how I understand your objective.
You have a div (#myDiv) which will retrieve it's initial HTML from the server.
You have an ajax function (getHtml) which retrieves this html and onSuccess updates #myDiv, possibly with this:
$('#myDiv').html(serverResponseHTMLContent);
You then have another function which may produce different HTML that should take the place of the server generated html.
If this is all correct then I would suggest you use knockout's html binding.
Your div would look like so.
<div id="myDiv" data-bind="html: myDivInnerHtml">
myDivInnerHtml would be part of your viewModel and should be an observable as you say you usually do.
Before the initial bind, call getHtml and have it set the value for myDivInnerHtml instead of actually setting the html for myDiv.
myDivInnerHtml = ko.observable(serverHtmlString);
Then when you apply the binding, myDiv's inner Html will be set by knockout.
To update the html, your client side function can change the value of myDivInnerHtml.
myDivInnerHtml(clientSideFunctionHtmlString);
If my assumptions are wrong and you have recreate the same html with different value, then you should use a template if possible and the server should not be sending the html, but instead the values to bind to the html.
Also, if the client side function is not creating html, but instead values to be bound to the html, then this will also not work.
You could look at the valueHasMutated() function which notifies subscribers that they should re-evaluate the observable.
See How to force a view refresh without having it trigger automatically from an observable? for a bit more explanation.

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