be-calculating (🧮)

be-calculating is basically the code-first counterpoint to the declarative be-observant enhancement, when the full power of the JavaScript run time engine is needed.

Part I Enhancing the output element with built in aggregators

Calculate value of the output element from peer input elements.

Example 1a Summing up

<form>
     <input type=range id=a name=a value=50>
    +<input type=number id=b name=b value=25>
    =

    <output name=result for="a b" 🧮=+></output>
</form>

What this does: The output element displays the sum of a and b, updated the moment the user changes either one of them. I.e. it is listening to the input events for a and b (and no other elements).

Other "built in" calculators are shown below:

| Operator | Notes | |----------|-----------------------| | + | Sums the args | | * | Product of the args | | max | Maximum f the args | | min | Minimum of the args |

Example 1b Multiplying

<form>
     <input type=range id=a name=a value=50>
    +<input type=number id=b name=b value=25>
    =

    <output name=result for="a b" 🧮=*></output>
</form>

Example 1c Maximizing

<form>
     <input type=range id=a name=a value=50>
    +<input type=number id=b name=b value=25>
    =

    <output name=result for="a b" 🧮=max></output>
</form>

Part II Custom calculations

Example 2a Global registry, function based

The developer can create a custom calculating function, as shown below. Doing so will cascade through the page into any ShadowDOM realms. The advantages is it makes it highly reusable. The thing to be cautious about is that it is "global" within the confines of all the elements adorned by the 🧮 attribute.

<script type=module>
    import {register} from '../🧮.js';
    register('linear', e => e.r = e.f.m * e.f.x + e.f.b );
</script>

<form>
    <label>
        m
        <input type=number id=m value=2>
    </label>
    <label>
        x
        <input type=number id=x value=2>
    </label>
        
    + <label>
        b
        <input type=number id=b value=25>
    </label>
    =

    <output name=result for="m x b" 🧮=linear></output>
</form>

In the javascript expression at the top, "f" stands for "factors", "r" for "result" or "return".

So the event provides the "f" property, which is basically factors we want to calculate based on -- the names (id's in this case) of the values.

But in some cases, we just want the array of arguments. In fact, the examples in part I were using reducers based on the args property of the event. So built in to 🧮 are registered event handlers such as

Registry.register(emc, '+', e => e.r = e.args.reduce((acc, arg) => acc + arg));

Example 2b Traditional local event handler

A framework or custom element host or local script element can attach a local event listener to the output element and compute the value

<form>
     <input type=range id=a name=a value=50>
    +<input type=number id=b name=b value=25>
    =

    <output id=output name=result for="a b" 🧮></output>
</form>
<script>
    output.addEventListener('calculate', e => e.r = e.f.m * e.f.x + e.f.b);
</script>

If the 🧮 emoji conflicts with another enhancement in the ShadowDOM root, look to this file to see how easy it is to take ownership of your own name.

BTW, the canonical name for this enhancement is the name of this package, be-calculating for more formal settings.

Part III - Customizing the dependencies

Example 3a Specify change (or other) default event

Up to now, we've been defaulting the event type to "input" as far as knowing when to update the calculation. But we can tweak that as shown below:

<form>
    <input type="range" id="a" value="50">
    +<input type="number" id="b" value="25">
    =<output for="a b" 🧮=+ 🧮-on=change ></output>
</form>

Alternative element references and/or event names for each observed element

Anything that requires subscribing to alternative or mixed event names, and/or that requires referencing nearby elements using something other than id's, needs to use an alternative to the for attribute. We do so by adopting DSS to describe what to observe, and optionally when to act.

Example 3b - References by n@me

<form>
    <input type="range" name=a value="50">
    +<input type="number" name=b value="25">
    =<output 🧮-for="@a and @b" 🧮=+></output>
</form>

This still happens to assume, by default, that the "input" event is what we should listen for, but having adopted DSS syntax, we can specify any other event name we may want. Id's and the for attribute are generated automatically by be-calculating in order to optimize our accessibility experience (if the for attribute/htmlFor property is found to be null/undefined).

Part IV Applied to non output elements

This enhancement also supports other elements.

Let's go in the opposite direction from before -- local to more global

Example 4a - Local script

Once again, a framework or custom element host or local script can work in partnership with be-calculating/🧮:

<input name=domain value=emojipedia.org>
<input name=search value=calculator>
<a id=link 🧮-for="@domain and @search">
    Emoji link
</a>
<script>
    link.addEventListener('calculate', e => e.r = `https://${e.f.domain}/search?q=${e.f.search}`)
</script>

Example 4b - Gain full access to the element

In the examples above, we engaged in "mind reading" in order to pass to the event handler the precise values we want to use in order to calculate the result.

The DSS syntax this package relies on allows us to override these mind readings, and specify which property to pass. The DSS feature that seems most useful in this context is probably:

Thanks but no thanks to all your "mind reading" -- could you please just pass in the dependent elements when they change, since I have full, unfettered access to the JavaScript engine, and I would like to extract things out of the elements that I please without your help?

To do so, specify this as follows:

<form>
    <input type="range" id="a" value="50">
    +<input type="number" id="b" value="25">
    =<output id=output 🧮-for="#a:$0 and #b:$0"></output>
    <script>
        output.addEventListener('calculate', e => e.r = e.f.a.valueAsNumber + e.f.b.valueAsNumber);
    </script>
</form>

In particular, DSS now supports :$0 to specify the element itself as the thing that needs passing.

Part V Scoped Handlers

Suppose you want to create reusable logic, but confined to the (repeatedly cloned) Shadow DOM Realm you are working with.

Example 5a Locally scoped handler

<my-element>
    <template shadowrootmode=open>
        <be-hive></be-hive>
        <form id=QkV8sbnus0SQPVBMxKuVLw>
            <script type=module>
                import {within} from 'be-calculating/🧮.js';
                within('#QkV8sbnus0SQPVBMxKuVLw', '^', e => e.r = e.f.a ** e.f.b);
            </script>
            <input type=range id=a name=a value=50>
            +<input type=number id=b name=b value=25>
            =
            <output name=result for="a b" 🧮=^></output>

        </form>
    </template>
</my-element>

Demo

Viewing Locally

Any web server that serves static files will do but...

1. Install git.
2. Fork/clone this repo.
3. Install node.
4. Open command window to folder where you cloned this repo.

5. npm install

6. npm run serve

7. Open http://localhost:3030/demo in a modern browser.

Importing in ES Modules:

import 'be-calculating/be-calculating.js';

Using from CDN:

<script type=module crossorigin=anonymous>
    import 'https://esm.run/be-calculating';
</script>