Bitovi

can-observation

Create observable values that derive their value from other observable values.

`new Observation( fn [, context][, options] )`

Creates an observable value from the return value of the given function called with this as the context.

The following creates a fullName observation that derives its values from the person observable.

import Observation from "can-observation";
import observe from "can-observe";

const person = observe( { first: "Ramiya", last: "Meyer" } );

const fullName = new Observation( function() {
    return person.first + " " + person.last;
} );

fullName.value; //-> "Ramiya Meyer";

fullName.on( function( newName ) {
    newName; //-> "Bodhi Meyer"
} );

person.first = "Bodhi";

Parameters

fn {function}:
The function whose value is being observed.
context {Object}:
What this should be when fn is called.
options {Object}:
An object that can configure the behavior of the observation with the following properties:
- priority {Number} - The priority this observation will be updated within can-queues.
- isObservable {Boolean} - If reading this observable should call add.

Use Cases

can-observation is used to derive values from other values without having to explicitly bind.

Use

To use can-observation, import it and create an observation that reads from other observables and returns a value.

The following creates a fullName observation that derives its values from the person observable.

import Observation from "can-observation";
import observe from "can-observe";

const person = observe( { first: "Ramiya", last: "Meyer" } );

const fullName = new Observation( function() {
    return person.first + " " + person.last;
} );

fullName.value; //-> "Ramiya Meyer";

fullName.on( function( newName ) {
    newName; //-> "Bodhi Meyer"
} );

person.first = "Bodhi";

Use [can-observation.prototype.off] to unbind.

How it works

when bound for the 1st time.
- calls fn between can-observation-recorder.start / stop to see what observables call OR.add.
- Binds to those using recorder-dependency-helpers
  - when a change happens, adds itself to the notify queue
    - repeats process