CODEWITHSUNDEEP
htmlknockout.jsknockout-3.0
bated
bated

Reputation: 960

How to validate knockout data-bind nestings?

Recently ran into a problem where knockout binding to html comments were not well formed because of a nesting problem. I used where an html comment to house a ko if: and then used ko foreach which was bound to an html <div>, but managed to get the nesting wrong. Below is an example of the issue:

<!-- ko if: isGuestCheckout() -->
     <div data-bind="foreach: formSection()">
<!-- /ko>
Simple malformed knockout</div>

In this simple example it is easy to see what the issue is, but in a much larger html block it is much harder to spot the error. I eventually resorted to have html comments for the end of each knockout binding for example <!-- end isGuestCheckout() --> which seems inefficient.

Is anyone aware of a way of validating that knockout data-binds are nested correctly?

Upvotes: 1

Views: 76

Answers (1)

Matthew Snyder
Matthew Snyder

Reputation: 448

I've run into similar issues and what I've done to troubleshoot in those cases is add a "whoami" observable for each nested KO-observable object and drop a simple span in the various nested levels to give me some insight as to what is being bound and where.

For example, if I have a view model like this...

var myViewModel = function() {
    var self = this;
    self.whoami = ko.observable("I am the root view model");
    self.items = ko.observableArray(); //This holds an array of myItem
};

var myItem = function() {
    var self = this;
    self.whoami = ko.observable("I am an item");
}

Then my HTML looks something like this...

<div>
    <!-- At this level I expect to see the whoami from the root VM -->
    <span data-bind="text: whoami"/>

    <div data-bind="foreach: listOfItems">
        <!-- At this level I expect to see the whoami from the item -->
        <span data-bind="text: whoami"/>
    </div>
</div>

Doing this has helped me quickly discover Knockout nesting issues. Once I find it then I just pull out the whoami span tags, but I usually end up keeping the whoami observable in the JS in case I need it again.

I hope this helps! :-)

Upvotes: 1

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