Click Binding adds click event to element on View. You can do click binding with any function in ViewModel or you can bind to any normal function.

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Let us try to understand it with a very simple ViewModel. We have a ViewModel as below

 var viewModel =
 {
 display: function ()
 {
 console.log("display");
 }
 }

As you see there is one function as property of ViewModel and that can be click bind on view as below,


<button data-bind="click:display" >display</button>

Let us consider one more example and in this we will update value of other observable on click of element on View. We have ViewModel as below,


var viewModel =
 {
 count : ko.observable(0) ,
 display: function ()
 {
 this.count( this.count() + 1);
 }
 }

On View we are doing click binding and text binding as below


<button data-bind="click:display" >display</button> <br/>
 Number of clicks <span data-bind="text:count" ></span>

Sometime you may have to pass current item in click binding. Assume a requirement that you have done foreach binding on element with observable array. Now on click of a particular item, you need to pass that item in ViewModel function to work with that. That can be solved as below. As you see in below ViewModel,

  • There is an observable array. This will be bind to ul or tr element on View
  • There is a function. It takes input which will be used to delete item from observable array.

function viewModel()
 {
 var self = this ;
 self.subject= ko.observableArray(["Phy", "Che", "Bio"]),
 self.removeSubject= function (item)
 {

 self.subject.remove(item);
 }
 }


ko.applyBindings(new viewModel());

On the View we need to do click binding and pass current item to function on which click binding is getting performed.


<ul data-bind="foreach: subject">
 <li>
 <span data-bind="text: $data"></span>
 <button data-bind="click: $parent.removeSubject">Remove</button>
 </li>
</ul>


If you notice we are passing current item using current binding context. So to pass current we are using parent.

In some scenario you will have to pass event object. Event object can be passed as given below,


function viewModel()
 {
 var self = this ;
 self.subject= ko.observableArray(["Phy", "Che", "Bio"]),
 self.removeSubject= function (data,event)
 {
 if (event.shiftKey) {
 self.subject.remove(data);
 }
 }
 }


On View binding can be done as below


<ul data-bind="foreach: subject">
 <li>
 <span data-bind="text: $data"></span>
 <button data-bind="click: $parent.removeSubject($data,event)">Remove</button>
 </li>
</ul>

&nbsp;

Now an item would be deleted on pressing shift key . Understanding of click binding is very useful to create apps using KO. I hope you find this post useful. Thanks for reading.

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2 thoughts on “Understanding click binding in Knockout.js

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