Question

I am using KnockoutJS to create a simple rotate animation. I have some items that contain a title and a description and I’m cycling trough these items.

Beneath the title and description I show some paging buttons and the active button should have a style applied.

However, the style for the paging button is not updated. Currently all paging buttons have the style applied instead of only styling the active page. I have created a jsFiddle that shows my problem.

What am I doing wrong?

JavaScript:

var AppViewModel = function () {
    this.currentItem = ko.observable();
    this.items = ko.observableArray([
    new Item("titleA", "descriptionA"),
    new Item("titleB", "descriptionB"), ]);

    this.tick = function () {
        var item = this.items.shift();
        if (item) {
            item.visible(false);
            this.items.push(item);
        }
        this.items()[0].visible(true);
    };

    this.tick();
    setInterval(function () {
        _this.tick();
    }, 1000);
}

var Item = function (title, description) {
    this.title = title;
    this.description = description;
    this.visible = ko.observable(false);
}

ko.applyBindings(new AppViewModel());

HTML:

<div data-bind="foreach: items">
    <div data-bind="visible:visible"> <span data-bind="text: title"></span>

        <blockquote data-bind="text: description"></blockquote>
    </div>
</div>
<nav>
    <ul data-bind="foreach: items">
        <li data-bind="style: { color: visible ? 'red' : 'black'} ">X</li>
    </ul>
</nav>

Answer 1

I think that when you are using an observable in a test condition, you need to call it properly, as otherwise what you asking it to resolve is whether visible is a truthy condition in js, which a function is:

<ul data-bind="foreach: items">
    <li data-bind="style: { color: visible() ? 'red' : 'black'} ">X</li>
</ul>

This seems to fix it for me in your jsFiddle.