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The checked binding links a checkable form control — i. When the user checks the associated form control, this updates the value on your view model. Likewise, when you update the value in your view model, this checks or unchecks the form control on screen.
Any previous checked state will be overwritten. For checkboxes , KO will set the element to be checked when the parameter value is true , and unchecked when it is false. This means that nonzero numbers and non- null objects and non-empty strings will all be interpreted as true , whereas zero, null , undefined , and empty strings will be interpreted as false.
When the user checks or unchecks the checkbox, KO will set your model property to true or false accordingly. Special consideration is given if your parameter resolves to an array. In this case, KO will set the element to be checked if the value matches an item in the array, and unchecked if it is not contained in the array.
When the user checks or unchecks the checkbox, KO will add or remove the value from the array accordingly. When the user changes which radio button is selected, KO will set your model property to equal the value of the selected radio button.
Of course, this is most useful when you have multiple radio button elements bound to a single model property. To ensure that only one of those radio buttons can be checked at any one time, you should set all of their name attributes to an arbitrary common value e. This is useful if you want the value to be something other than a string such as an integer or object , or you want the value set dynamically. In the following example, the item objects themselves not their itemName strings will be included in the chosenItems array when their corresponding checkboxes are checked:.
If your checkedValue parameter is an observable value, whenever the value changes and the element is currently checked, the binding will update the checked model property. For checkboxes, it will remove the old value from the array and add the new value. For radio buttons, it will just update the model value. Extending the binding syntax Components Overview: What components and custom elements offer Defining and registering components The component binding Using custom elements Advanced: The "checked" binding Purpose The checked binding links a checkable form control — i.