Knockout select change

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Stack Overflow for Teams is a private, secure spot for you and your coworkers to find and share information. I am building a permissions UI, I have a list of permissions with a select list next to each permission. The permissions are represented by an observable array of objects which are bound to a select list:.

knockout select change

Now the problem is this: the change event gets raised when the UI is just populating for the first time. I call my ajax function, get the permissions list and then the event get raised for each of the permission items. This is really not the behavior I want. I want it to be raised only when a user really picks out a new value for the permission in the select listhow can I do that?

Actually you want to find whether the event is triggered by user or programand its obvious that event will trigger while initialization.

The knockout approach of adding subscription won't help in all cases, why because in most of the model will be implemented like this. The actual step that we want to capture is changes in 3, but in second step subscription will get callSo a better way is to add to event change like. This is just a guess, but I think it's happening because level is a number.

In that case, the value binding will trigger a change event to update level with the string value. You can fix this, therefore, by making sure level is a string to start with. Additionally, the more "Knockout" way of doing this is to not use event handlers, but to use observables and subscriptions. Make level an observable and then add a subscription to it, which will get run whenever level changes. Here is a solution that may help with this strange behaviour.

I couldn't find a better solution than place a button to manually trigger the change event. I use this custom binding based on this fiddle by RP Niemeyer, see his answer to this questionwhich makes sure the numeric value is properly converted from string to number as suggested by the solution of Michael Best :.

If you use an observable instead of a primitive value, the select will not raise change events on initial binding. You can continue to bind to the change event, rather than subscribing directly to the observable. If this doesn't work, try wrapping the last line in a setTimeout - events are async, so maybe the last one is still pending when applyBindings already returned.By using our site, you acknowledge that you have read and understand our Cookie PolicyPrivacy Policyand our Terms of Service.

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When adding a change event binding to an input box using knockout. I can work around this by using blur. Is this the intended behavior?

Is the idea to use the change event to have the old value and then use a normal selector to get the value from the dom? It seems counter intuitive. Update: For newer versions of knockout, you can replace the value binding with textInputwhich handles many edge cases not covered by valueUpdate.

knockout select change

If you want to push the new value in as the user types, using the valueUpdate option of the input binding:. The valueUpdate option takes an event name e. Still do the valueUpdate binding like I showed above, but instead of listening for the changed event, just subscribe to the observable:.

Also note that when you make use of subscribe to an observable, it gets triggered every time your value changes. Learn more.

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Asked 8 years, 1 month ago. Active 2 years, 1 month ago. Viewed 66k times. Ominus Ominus 4, 6 6 gold badges 30 30 silver badges 42 42 bronze badges. Active Oldest Votes. No, this is not the right way to do things. Now let me propose an alternate solution.

I have to use 'afterkeydown', otherwise I'm one character late. Is there a reason why not using the textInput binding? The documentation of KO recommends to use the textInput binding instead of the value binding : knockoutjs. The reason is that this answer was written before textinput binding existed. Updated the answer to use the new textInput binding. If you put the 'event' option at the end you don't need the 'valueUpdate' option.

Fragy Fragy 2 2 bronze badges.By using our site, you acknowledge that you have read and understand our Cookie PolicyPrivacy Policyand our Terms of Service. The dark mode beta is finally here. Change your preferences any time. Stack Overflow for Teams is a private, secure spot for you and your coworkers to find and share information. I have a problem with one select element.

I create a binding for the change event, and it works when I change the selected element manually, but if the select element is binding with a specified value, the change function is not call. I need it so that if the property myfield has a value different to '' the change function will execute.

You're having trouble because you're fighting Knockout, not using it here You should read through the selectedOptions documentation and options bindingor perhaps even do some of the KO tutorials. Basically, you never want to handle the change event for DOM elements yourself. In addition, Knockout should also be in charge of generating the option s for you.

If you actually need to subscribe to a change in the dropdown, subscribe to the myfield changes instead as shown above. Learn more. Asked 5 years, 7 months ago. Active 5 years, 7 months ago. Viewed 17k times. Julito Avellaneda. Julito Avellaneda Julito Avellaneda 2, 2 2 gold badges 14 14 silver badges 22 22 bronze badges. I am trying to understand your problem.

Can you explain this part of your question, can you give some details? Active Oldest Votes. Jeroen Jeroen 48k 27 27 gold badges silver badges bronze badges.

Hi Jeroen, you are right, I'm no using ko so good, but now I cannot do so many changes to do a good binding talk with the PM :so for this reason I need to do a "fix", maybe you have any idea?

The easiest way to fix this is to use KO correctly. Any other solution will be much more work IMO. JulitoAvellaneda From what I read, the self. It's also not a drastic change to your existing code. Sign up or log in Sign up using Google. Sign up using Facebook. Sign up using Email and Password. Post as a guest Name. Email Required, but never shown.

The Overflow Blog. Featured on Meta. Community and Moderator guidelines for escalating issues via new response….The selectedOptions binding controls which elements in a multi-select list are currently selected.

When the user selects or de-selects an item in the multi-select list, this adds or removes the corresponding value to an array on your view model. Note: To control which element in a single-select drop-down list is selected, you can use the value binding instead. This should be an array or an observable array.

KnockoutJS - Options Binding

Any previous selection state will be overwritten. Whether or not the parameter is an observable array, KO will detect when the user selects or deselects an item in the multi-select list, and will update the array to match.

This is how you can read which of the options is selected. In the example code above, the user can choose from an array of string values. See the options binding for details on how to control how arbitrary objects should be displayed in the list. In this scenario, the values you can read and write using selectedOptions are those objects themselves, not their textual representations.

This leads to much cleaner and more elegant code in most cases. Your view model can imagine that the user chooses from an array of arbitrary objects, without having to care how those objects are mapped to an on-screen representation. The "selectedOptions" binding Purpose The selectedOptions binding controls which elements in a multi-select list are currently selected.This binding is used to define the options for a select element.

This can be used for either drop-down list or a multi-select list. Parameter to be passed here is an array. For each entry in array, the option will be added for respective select node. Earlier option will be removed. If the parameter is an observable value, then the element's available options will be updated as and when the underlying observable is changed. Element is processed only once, if no observable is used.

This parameter can also include a function, which returns the property to be used.

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This parameter allows to specify which object property can be used to set the value attribute of the option elements. This way one can keep default option as blank when the user views drop-down for the very first time.

For a single select in the drop-down list, the previously selected value will still be preserved. For multi select list, all previously selected options will be preserved. The generated options can be post processed for some further custom logic with the help of optionsAfterRender callback. Let us take a look at the following example which uses optionsAfterRender to add a disable binding to each option.

knockout select change

Previous Page. Next Page. Live Demo. Previous Page Print Page.The event binding allows you to add an event handler for a specified event so that your chosen JavaScript function will be invoked when that event is triggered for the associated DOM element. This can be used to bind to any event, such as keypressmouseover or mouseout.

Now, moving your mouse pointer on or off of the first element will invoke methods on the view model to toggle the detailsEnabled observable. The second element reacts to changes to the value of detailsEnabled by either showing or hiding itself. You should pass a JavaScript object in which the property names correspond to event names, and the values correspond to the function that you want to bind to the event.

When calling your handler, Knockout will supply the current model value as the first parameter. For example. In some scenarios, you may need to access the DOM event object associated with your event. Knockout will pass the event as the second parameter to your function, as in this example:.

If you need to pass more parameters, one way to do it is by wrapping your handler in a function literal that takes in a parameter, as in this example:.

Now, KO will pass the event to your function literal, which is then available to be passed to your handler. Alternatively, if you prefer to avoid the function literal in your view, you can use the bind function, which attaches specific parameter values to a function reference:.

By default, Knockout will prevent the event from taking any default action. However, if you do want to let the default action proceed, just return true from your event handler function. By default, Knockout will allow the event to continue to bubble up to any higher level event handlers.

For example, if your element is handling a mouseover event and a parent of the element also handles that same event, then the event handler for both elements will be triggered. If necessary, you can prevent the event from bubbling by including an additional binding that is named youreventBubble and passing false to it, as in this example:.

Normally, in this case myButtonHandler would be called first, then the event would bubble up to myDivHandler. However, the mouseoverBubble binding that we added with a value of false prevents the event from making it past myButtonHandler. Knockout will use jQuery, if it is present, for handling UI events. To disable this behavior and instruct Knockout to always use native event handling, you can set the following option in your code before calling ko.

The "event" binding Purpose The event binding allows you to add an event handler for a specified event so that your chosen JavaScript function will be invoked when that event is triggered for the associated DOM element.The options binding controls what options should appear in a drop-down list i.

The value you assign should be an array or observable array. Note: For a multi-select list, to set which of the options are selected, or to read which of the options are selected, use the selectedOptions binding. For a single-select list, you can also read and write the selected option using the value binding. Note that the only difference between examples 3 and 4 is the optionsText value. You should supply an array or observable array. Any previous options will be removed.

However, if you want to let the user choose from an array of arbitrary JavaScript objects not merely stringsthen see the optionsText and optionsValue parameters below.

Sometimes, you might not want to select any particular option by default. But a single-select drop-down list usually starts with some item selected, so how can you avoid preselecting something? This easy to do: just add an additional parameter with name optionsCaptionwith its value being a string to display.

For example:. So, if myChosenValue holds the value undefined which observables do by defaultthen the dummy option will be selected. See Example 3 above to see how you can bind options to an array of arbitrary JavaScript object - not just strings. Example 3 shows how you can specify that property name by passing an additional parameter called optionsText. See Example 4 above, which shows how you could generate the displayed text by concatenating together multiple property values.

You can also specify a JavaScript function to determine this value. Sometimes you may want to mark an array entry as deleted, but without actually losing record of its existence. This is known as a non-destructive delete. For details of how to do this, see the destroy function on observableArray. By default, the options binding will skip over i.

knockout select change

If you want to show destroyed entries, then specify this additional parameter like:. If you need to run some further custom logic on the generated option elements, you can use the optionsAfterRender callback.

See Note 2 below. For a multi-select list, you can read and write the selection state using selectedOptions. Technically this is a separate binding, so it has its own documentation.


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