Bindable setter patterns

Use bindable property setters to transform incoming values before Aurelia applies them.

In some cases, you want to make an impact on the value that is binding. For such a scenario you can use the possibility of new set.

@bindable({ 
    set: value => someFunction(value),  /* HERE */
    // Or set: value => value,
    mode: /* ... */ 
})

Suppose you have a carousel component in which you want to enable navigator feature for it. You probably imagine such a thing for yourself.

<!-- Enable -->
<my-carousel navigator.bind="true">
<my-carousel navigator="true">
<my-carousel navigator=true>
<my-carousel navigator>

<!-- Disable -->
<my-carousel navigator.bind="false">
<my-carousel navigator="false">
<my-carousel navigator=false>
<my-carousel>

In version two, you can easily implement such a capability with the set feature.

To make things easier, first design a new type that accepts true and false as a string and a boolean.

export type BooleanString = "true" | "false" | true | false /* boolean */;

Define your property like this:

@bindable({ set: /* ? */, mode: BindingMode.toView }) public navigator: BooleanString = false;

For set part, we need functionality to check the input, If the value is one of the following, we want to return true, otherwise we return the false value.

• '': No input for a standalone navigator property.

• true: When the navigator property set to true.

• "true": When the navigator property set to "true".

So our function will be like this

export function truthyDetector(value: unknown) {
    return value === '' || value === true || value === "true";
}

Now, we should set truthyDetector function as following:

@bindable({ set: truthyDetector, mode: BindingMode.toView }) public navigator: boolean = false;

Although, there is another way to write the functionality too

@bindable({ set: v => v === '' || v === true || v === "true", mode: BindingMode.toView }) public navigator: boolean = false;

You can simply use any of the above four methods to enable/disable your feature.