Develop Reference

binding multi dropdown list in knockout.js

I have a multi dropdown list and I need to do the following:
1. Make sure that when selecting value in one dropdown list it won't appear in the others (couldn't find a proper solution here).
2. When selecting the value "Text" a text field (<input>) will apear instead of the Yes/no dropdown.
3. "Choose option" will appear only for the first row (still working on it).
4. Make sure that if "Text" is selected, it always will be on the top (still working on it).
JSFiddle
HTML:
<div class='liveExample'>
<table width='100%'>
<tbody data-bind='foreach: lines'>
<tr>
<td>
Choose option:
</td>
<td>
<select data-bind='options: filters, optionsText: "name", value: filterValue'> </select>
</td>
<td data-bind="with: filterValue">
<select data-bind='options: filterValues, optionsText: "name", value: "name"'> </select>
</td>
<td>
<button href='#' data-bind='click: $parent.removeFilter'>Remove</button>
</td>
</tr>
</tbody>
</table>
<button data-bind='click: addFilter'>Add Choice</button>
JAVASCRIPT:
var CartLine = function() {
var self = this;
self.filter = ko.observable();
self.filterValue = ko.observable();
// Whenever the filter changes, reset the value selection
self.filter.subscribe(function() {
self.filterValue(undefined);
});
};
var Cart = function() {
// Stores an array of filters
var self = this;
self.lines = ko.observableArray([new CartLine()]); // Put one line in by default
// Operations
self.addFilter = function() { self.lines.push(new CartLine()) };
self.removeFilter = function(line) { self.lines.remove(line) };
};
ko.applyBindings(new Cart());
I will appeaciate your assist here! Mainly for the first problem.
Thanks!
Mike

If you want to limit the options based on the options that are already selected in the UI, you'll need to make sure every cartLine gets its own array of filters. Let's pass it in the constructor like so:
var CartLine = function(availableFilters) {
var self = this;
self.availableFilters = availableFilters;
// Other code
// ...
};
You'll have to use this new viewmodel property instead of your global filters array:
<td>
<select data-bind='options: availableFilters,
optionsText: "name",
value: filterValue'> </select>
</td>
Now, we'll have to find out which filters are still available when creating a new cartLine instance. Cart manages all the lines, and has an addFilter function.
self.addFilter = function() {
var availableFilters = filters.filter(function(filter) {
return !self.lines().some(function(cartLine) {
var currentFilterValue = cartLine.filterValue();
return currentFilterValue &&
currentFilterValue.name === filter.name;
});
});
self.lines.push(new CartLine(availableFilters))
};
The new CartLine instance gets only the filter that aren't yet used in any other line. (Note: if you want to use Array.prototype.some in older browsers, you might need a polyfill)
The only thing that remains is more of an UX decision than a "coding decision": do you want users to be able to change previous "Choices" after having added a new one? If this is the case, you'll need to create computed availableFilters arrays rather than ordinary ones.
Here's a forked fiddle that contains the code I posted above: http://jsfiddle.net/ztwcqL69/ Note that you can create doubled choices, because choices remain editable after adding new ones. If you comment what the desired behavior would be, I can help you figure out how to do so. This might require some more drastic changes... The solution I provided is more of a pointer in the right direction.
Edit: I felt bad for not offering a final solution, so here's another approach:
If you want to update the availableFilters retrospectively, you can do so like this:
CartLines get a reference to their siblings (the other cart lines) and create a subscription to any changes via a ko.computed that uses siblings and their filterValue:
var CartLine = function(siblings) {
var self = this;
self.availableFilters = ko.computed(function() {
return filters.filter(function(filter) {
return !siblings()
.filter(function(cartLine) { return cartLine !== self })
.some(function(cartLine) {
var currentFilterValue = cartLine.filterValue();
return currentFilterValue &&
currentFilterValue.name === filter.name;
});
});
});
// Other code...
};
Create new cart lines like so: self.lines.push(new CartLine(self.lines)). Initiate with an empty array and push the first CartLine afterwards by using addFilter.
Concerning point 2: You can create a computed observable that sorts based on filterValue:
self.sortedLines = ko.computed(function() {
return self.lines().sort(function(lineA, lineB) {
if (lineA.filterValue() && lineA.filterValue().name === "Text") return -1;
if (lineB.filterValue() && lineB.filterValue().name === "Text") return 1;
return 0;
});
});
Point 3: Move it outside the foreach.
Point 4: Use an if binding:
<td data-bind="with: filterValue">
<!-- ko if: name === "Text" -->
<input type="text">
<!-- /ko -->
<!-- ko ifnot: name === "Text" -->
<select data-bind='options: filterValues, optionsText: "name", value: "name"'> </select>
<!-- /ko -->
<td>
Updated fiddle that contains this code: http://jsfiddle.net/z22m1798/

Knockout multiple click bindings do not work with IE8

The problem:
Multiple click binding do not work in IE8.
The code:
var Cart = function() {
var self = this;
self.books = ko.observableArray();
self.cds = ko.observableArray();
};
var TheModel = function() {
var self = this;
self.cart = ko.observable(new Cart());
self.showAddBook = function() {
self.cart.books.push(/* new book */);
};
self.showAddCD = function() {
self.cart.cds.push(/* new cd */);
};
};
<div data-bind="with: cart">
<h1>Books<h1>
<button data-bind="click: $parent.showAddBook">Add</button>
<div data-bind="foreach: books">
<span data-bind="text: name"></span> <!-- book has a name property -->
</div>
<hr/>
<h3>CDs</h3>
<button data-bind="click: $parent.showAddCD">Add</button>
<div data-bind="foreach: cds">
<span data-bind="text: name"></span> <!-- cd has a name property -->
</div>
</div>
Background:
Apologies in advance. I don't have access to jsFiddle at work.
I have a deadline to get this piece of work complete which is why I am using knockout with jQuery. Would love to use Angular but can't because we have to support IE8. Would love to use Durandal but I have no experience of it and don't have the time just yet to learn it and finish this piece of work.
A user can create a new book or a new cd and add it to a collection. Not real-world example but reflects the problem I am solving.
A user can click on an Add button, this launches a jQuery dialog which captures some information about a book. This is then saved to the observable array on the model, and the list of books gets updated.
Question:
Why does IE8 only seem to bind the first click and not the second? If I click to add a book the dialog is shown. If I click to add a cd, nothing. I have debugged and the function does not get called.
TIA

As far as I can tell, neither of them should work, and not on any browser (rather than just not working on IE8), because both functions have the same problem: They don't unwrap cart:
self.cart.books.push(/* new book */);
// ^^^^^^
cart is an observable, so you need:
self.cart().books.push(/* new book */);
// ^^
...and similarly for the CDs stuff.
If you fix that, it works (even on IE8):
var Cart = function() {
var self = this;
self.books = ko.observableArray();
self.cds = ko.observableArray();
};
var TheModel = function() {
var self = this;
self.cart = ko.observable(new Cart());
self.showAddBook = function() {
self.cart().books.push({name: "New book " + (+new Date())});
};
self.showAddCD = function() {
self.cart().cds.push({name: "New CD " + (+new Date())});
};
};
ko.applyBindings(new TheModel(), document.body);
<div data-bind="with: cart">
<h1>Books<h1>
<button data-bind="click: $parent.showAddBook">Add</button>
<div data-bind="foreach: books">
<span data-bind="text: name"></span> <!-- book has a name property -->
</div>
<hr/>
<h3>CDs</h3>
<button data-bind="click: $parent.showAddCD">Add</button>
<div data-bind="foreach: cds">
<span data-bind="text: name"></span> <!-- cd has a name property -->
</div>
</div>
<script src="https://cdnjs.cloudflare.com/ajax/libs/knockout/3.2.0/knockout-min.js"></script>
<script src="https://ajax.googleapis.com/ajax/libs/jquery/1.11.1/jquery.min.js"></script>

Apologies for slightly incorrect example but I had missed one level of nesting. My example is not a true reflection of my complex model and implementation but I worked out the cause of the problem.
My Cart in this example has a selectedItem property (an observable) of type object that has the array of books (observable array) and CDs (observable array).
var Items = function () {
this.books = ko.observableArray();
this.cds = ko.observableArray();
}
var Cart = function() {
this.selectedItem = ko.observable(new Items());
}
var Model = function () {
this.cart = new Cart();
}
I was using the knockout 'with' binding and setting the context to cart.selectedItem
<div data-bind="with: cart.selectedItem"> ... </div>
With this approach I noticed that only the first click (add book) was working. Clicking on Add CD was doing nothing.
I changed the context from cart.selectedItem to cart and set the foreach binding (that displays the list of books and cds) to selectedItem().books and selectedItem().cds and that worked in IE8 and other browser.
If I change the context using the knockout 'with' binding back to cart.selectedItem then only the first click works.
Hope that helps anyone else who encounters this problem.

Populate knockout view model from javascript

I'm in the process of replacing one hell of a lot of javascript/jquery code with knockoutjs and I'm trying to figure out the best way forward. I have no time to replace everything at the same time so I will have to integrate the knockout logic with the existing javascript...
Is there a way to populate a knockout view model from javascript which is not called from a data-bind attribute? Any help would be nice since I've not been able to find this anywhere else (at least not anything that worked).
I know what I'm mentioning here isn't the "correct" way of doing things, but I'm trying to migrate parts of the javascript code... Doing it all in one go isn't an option at the moment.
(using knockout 3.2)
Edit:
Typically the existing javascript does something like:
$('#productlist').append(productItemHtmlCode);
And I would rather have it do something like:
ViewModel.productList.push(productItemObject);

If I understand correctly, currently you have something like this:
<div id='myDiv'>
current status is: <span id='statusSpan'>Active</span>
</div>
with some corresponding javascript that might be something like:
function toggleStatus() {
var s= document.getElementById('statusSpan');
s.innerHTML = s.innerHTML == 'Active' ? 'Inactive' : 'Active';
}
And you want to change it so that the javascript is updating the viewmodel rather than manipulating the DOM?
var app = (function() {
var vm = {
statusText: ko.observable('Active'),
toggleStatus: toggleStatus
}
return vm
function toggleStatus() {
vm.statusText = vm.statusText == 'Active' ? 'Inactive' : 'Active';
}
}) ();
ko.applyBindings(app,document.getElementById('myDiv'));
And then the html would be
<div id='myDiv'>
current status is: <span id='statusSpan' data-bind="text: statusText"></span>
</div>
If that's what you're talking about, that's what Knockout is designed for. The javascript updates the viewmodel, knockout manipulates the DOM.
The example you give is easy to represent in Knockout.
the HTML:
<div>
<table data-bind="foreach: products">
<tr>
<td data-bind="text: id"></td>
<td data-bind="text: name"></td>
<td data-bind="text: category"></td>
</tr>
</table>
</div>
and in the viewmodel:
vm = {
products: ko.observableArray(), // empty array to start
addProduct: addProduct
}
return vm;
function addProduct(id, name, category) {
products.push({id: id, name: name, category:category});
}
etc.

Knockout: Best way to bind visibility to both item and a parent property?

I am creating an edit screen where I want people to delete items from a list. The list is displayed normally, until the "controller" object goes into edit mode. Then the user can delete items. Items should be flagged for deletion and displayed as such, then when the user saves the edit, they are deleted and the server notified.
I actually have this all working, but the only way I could do it was using literal conditions in the bindings, which looks ugly and I don't really like. Is there a better way of doing it?
Working Fiddle: http://jsfiddle.net/L1e7zwyv/
Markup:
<div id="test">
<a data-bind="visible: IsViewMode, click: edit">Edit</a>
<a data-bind="visible: IsEditMode, click: cancel">Cancel</a>
<hr/>
<ul data-bind="foreach: Items">
<li data-bind="css: CssClass">
<span data-bind="visible: $parent.IsViewMode() || $data._Deleting(), text: Value"></span>
<!-- ko if: $parent.IsEditMode() && !$data._Deleting() -->
<input type="text" data-bind="value: Value"/>
<a data-bind="click: $parent.deleteItem">Del</a>
<!-- /ko -->
</li>
</ul>
</div>
Code:
function ItemModel(val)
{
var _this = this;
this.Value = ko.observable(val);
this._Deleting = ko.observable();
this.CssClass = ko.computed(
function()
{
return _this._Deleting() ? 'deleting' : '';
}
);
}
function ManagerModel()
{
var _this = this;
this.Items = ko.observableArray([
new ItemModel('Hell'),
new ItemModel('Broke'),
new ItemModel('Luce')
]);
this.IsEditMode = ko.observable();
this.IsViewMode = ko.computed(function() { return !_this.IsEditMode(); });
this.edit = function(model, e)
{
this.IsEditMode(true);
};
this.cancel = function(model, e)
{
for(var i = 0; i < _this.Items().length; i++)
_this.Items()[i]._Deleting(false);
this.IsEditMode(false);
};
this.deleteItem = function(model, e)
{
model._Deleting(true);
};
}
ko.applyBindings(new ManagerModel(), document.getElementById('test'));

you could:
wrap another span around to separate the bindings but this would be less efficient.
use both a visible: and if: binding on the same element to achieve the same functionality,
write a function on the itemModel isVisible() accepting the parent as an argument making your binding visible: $data.isVisible($parent).
Afterthought: If this comes up in multiple places you could write a helper function to combine visibility bindings
// reprisent variables from models
var v1 = false;
var v2 = false;
var v3 = false;
// Helper functions defined in main script body - globally accessible
function VisibilityFromAny() {
var result = false;
for(var i = 0; i < arguments.length; i++ ) result |= arguments[i];
return Boolean(result);
}
function VisibilityFromAll() {
var result = true;
for(var i = 0; i < arguments.length; i++ ) result &= arguments[i];
return Boolean(result);
}
// represent bindings
alert(VisibilityFromAny(v1, v2, v3));
alert(VisibilityFromAll(v1, v2, v3));
The third option is the most popular technique with MVVM aficionados like yourself for combining variables in a single binding from what I've seen, it makes sense and keeps all the logic away from the view markup in the view models.
Personally I like the syntax you have at present, (even though I count myself amongst the MVVM aficionado gang as well) this clearly shows in the view markup that the visibility of that element is bound to 2 items rather then hiding these details in a function.

I try to think of view models as a model for my view, not just a place where logic resides. When possible I also try to move complex logic back the view model and use descriptive names for my variables so the code is more readable.
I would suggest adding this to your view model -
var isViewable = ko.computed(function () { return IsViewMode() || _Deleting(); });
var isEditable = ko.computed(function() { return IsEditMode() && !_Deleting(); });
And in your view -
<li data-bind="css: CssClass">
<span data-bind="visible: isViewable, text: Value"></span>
<!-- ko if: isEditable -->
<input type="text" data-bind="value: Value"/>
<a data-bind="click: $parent.deleteItem">Del</a>
<!-- /ko -->
</li>
This cleans the bindings up and allows you to more easily adjust the logic without having to do many sanity checks in your view and view model both. Also I personally name variables that return a boolean such as this as isWhatever to help be more descriptive.
The benefit is that as your view and view model grow larger you can keep the DOM clean of clutter and also your view model becomes testable.
Here is a 'code complete' version of your fiddle with this added -
http://jsfiddle.net/L1e7zwyv/3/

binding knockout observable arrays to multiple <ul> elements

For a navigation menu, I have two groups of links, each group and link showing up or not dependent on a user's role. The roles are looked up when the link structure is being built and the list of links is built accordingly. The returned JSON gets parsed, put into observable arrays with no problem, but when I actually try and apply the bindings, the binding fails because the observables are blank. Here is the HTML...
<ul id="user-menu" class="menu" data-bind="foreach: areas">
<li>
<a data-bind="attr: { href: areaLink }">
<img data-bind="attr: { src: iconUri }" />
<span data-bind="text: areaName"></span>
</a>
</li>
</ul>
<ul id="admin-menu" class="menu" data-bind="foreach: adminAreas">
<li>
<a data-bind="attr: { href: areaLink }">
<img data-bind="attr: { src: iconUri }" />
<span data-bind="text: areaName"></span>
</a>
</li>
</ul>
Knockout view model in the background...
var navigation = (function() {
function Area() {
var self = this;
self.areaName = ko.observable();
self.areaLink = ko.observable();
self.iconUri = ko.observable();
self.sequenceNo = ko.observable();
self.isAdmin = ko.observable();
self.loadFromVM = function (vm) {
self.areaName(vm.name || '');
self.areaLink(vm.link || '');
self.iconUri(vm.iconUri || '');
self.sequenceNo(vm.sequenceNo || '');
self.isAdmin(vm.isAdmin);
}
}
function viewModel() {
var self = this;
self.areas = ko.observableArray([]);
self.adminAreas = ko.observableArray([]);
self.setup = function () {
var data = {}; // population with basic session data
$.getJSON('....php', { JSON.stringify(data) }, function (results) {
for (var i = 0; i < results.length; i++) {
var area = new Area();
area.loadFromVM(results[i]);
if (area.isAdmin()) {
self.adminAreas().push(area);
} else {
self.areas().push(area);
}
}
});
};
}
var vmInstance;
return {
setup: function () {
vmInstance = new viewModel();
vmInstance.setup();
ko.applyBindings(vmInstance, $('#user-menu')[0]);
ko.applyBindings(vmInstance, $('#admin-menu')[0]);
}
};
})();
And then I bring it together with this in the navigation view file...
navigation.setup();
So after I get my JSON back, parse it, and organize it when I loop through the success function of the $.getJSON method, putting a watch on self.areas() and self.adminAreas() does show that the arrays have the exact information I want them to. But by the time they have to be applied, calling vmInstance.areas().length or vmInstance.adminAreas().length returns zero. Even more oddly, putting in an alert with the length of the arrays right after the $.getJSON call but within the setup() function will cause the alert to fire first, show zeroes, then goes through the get, populates the array, then fires zeroes again.
Not exactly sure what's going on here, but I can't remember seeing this kind of behavior in another project so I'm not quite sure what I'm doing wrong here. Any ideas or advice would be greatly appreciated.
EDIT: Nevermind on the Fiddle. It doesn't really capture my actual error.

adminarea object is not initialized.you made the adminArea variable but instead of this you have used same area variable to set values.
var adminArea = new Area();
adminArea.areaName('test admin area');
adminArea.areaLink('#');
adminArea.iconUri('http://evernote.com/media/img/getting_started/skitch/windows8/win8-checkmark_icon.png');
adminArea.sequenceNo(1);
adminArea.isAdmin(true);
Fiddle Demo