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TwitterreturnedBy
Creates an observable that derives its value from other observable values.
value.returnedBy( getter(), context )
Creates an observable value that can be read and observed using can-reflect.
The following creates a fullName observable that derives its values from the
person observable. The value of the observable is read with fullName.value:
import { value, Reflect as canReflect } from "can";
const first = value.with("Grace");
const last = value.with("Murray");
const fullName = value.returnedBy(() => {
return first.value + " " + last.value;
});
console.log(fullName.value); //-> "Grace Murray"
const handler = newValue => {
console.log(newValue); //-> "Grace Hopper"
};
canReflect.onValue(fullName, handler);
last.value = "Hopper";
Parameters
- getter
{function}:A function that returns the value being observed.
- context
{Object}:An optional context that will be used as the
thisofgetter.
Returns
{Object}:
An observable compatible with getValue. It also has a value property that can
be used to get and set the value.
value.returnedBy( getter(lastSet), context, initialValue )
Creates an observable value that can be set. When the getter function takes an
argument, the getter function will be passed whatever the observable was last set to.
This form is similar to with. But it can be used to "clean up" values as follows:
import { value } from "can";
var age = value.returnedBy(function(lastSet){
return lastSet == null ? 0 : +lastSet;
});
console.log(age.value); //-> 0
age.value = "5";
console.log(age.value); //-> 5
Parameters
- getter
{function(lastSet)}:A function that returns the value being observed.
- context
{Object}:An optional context that will be used as the
thisofgetter. - initialValue
{Object}:The initial
lastSetvalue.