Bitovi

can-attribute-observable

Create an observable value from an element's property or attribute.

`new AttributeObservable(element, key, event)`

import {AttributeObservable, Symbol as canSymbol} from "can";

var input = document.querySelector("input");
var obs = new AttributeObservable(input, "value", "input");

obs[canSymbol.for("can.onEmit")](function(value){
  console.log("updated", value);
});

Parameters

element {HTMLElement}:
key {String}:
A property or attribute name.
event {String}:

Use

The Forms guide is a great place to see how these are used internally by CanJS.

Special Keys

AttributeObservable allows you to specify the following special key values:

Focused

If the value is focused or not:

<my-demo></my-demo>
<style>
:focus { background-color: yellow; }
</style>
<script type="module">
import { StacheElement } from "can";

class MyDemo extends StacheElement {
    static view = `
        <input
            on:input:value:bind="this.cardNumber"
            placeholder="Card Number (9 digits)"/>
        <input size="4"
            on:input:value:bind="this.cvcNumber"
            focused:from="this.cvcFocus"
            on:blur="this.dispatch('cvcBlur')"
            placeholder="CVC"/>
        <button
            focused:from="this.payFocus"
            on:blur="this.dispatch('payBlur')">Pay</button>
    `;
    static props = {
        cardNumber: String,
        cvcNumber: String,
        cvcFocus: {
            value({listenTo, resolve}) {
                listenTo("cardNumber", (ev, newVal) => {
                    if(newVal.length === 9) {
                        resolve(true);
                    } else {
                        resolve(false);
                    }
                });
                listenTo("cvcBlur", () => {
                    resolve(false);
                });
            }
        },
        payFocus: {
            value({listenTo, resolve}) {
                listenTo("cvcNumber", (ev, newVal) => {
                    if(newVal.length === 3) {
                        resolve(true);
                    } else {
                        resolve(false);
                    }
                });
                listenTo("payBlur", () => {
                    resolve(false);
                });
            }
        }       
    };
}
customElements.define('my-demo', MyDemo);
</script>

Values

Get the checked <options> as an array:

<pizza-toppings-picker></pizza-toppings-picker>
<style>
:focus { background-color: yellow; }
</style>
<script type="module">
import { StacheElement } from "can";

class PizzaToppingsPicker extends StacheElement {
    static view = `
        <label>
            What pizza toppings do you like?
            <select values:bind="this.toppings" multiple>
                <option>Pepperoni</option>
                <option>Mushrooms</option>
                <option>Onions</option>
                <option>Sausage</option>
                <option>Bacon</option>
                <option>Extra cheese</option>
                <option>Black olives</option>
                <option>Green peppers</option>
                <option>Pineapple</option>
                <option>Spinach</option>
            </select>
        </label>

        <p>
            Selected toppings:
            {{# for( topping of this.toppings) }}
                {{ topping }}
            {{/ for }}
        </p>    
    `;
    static props = {
        toppings: { 
            get default() {
                return [];
            }
        }
    };
}
customElements.define('pizza-toppings-picker', PizzaToppingsPicker);
</script>