Toggler

Toggler is a tool to asynchronously toggle between two operations, using throttled/debounced task scheduling.

For example, managing the showing and hiding of a modal (UI blocking) spinner:

var toggle = Toggler(
    /*taskOneDelay=*/250,
    /*taskTwoDelay=*/100
);

// (throttled) toggle on the spinner
toggle(showSpinner,hideSpinner);

// later, (throttled) toggle off the spinner
toggle(showSpinner,hideSpinner);

Note: This example illustrates asynchronously toggling between showing a spinner and hiding it, with throttling/debouncing and cancellation all managed internally.

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Library Tests (Demo)

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Overview

The main purpose of Toggler is to manage scheduling (throttling/debouncing) when asynchronously toggling between two tasks.

Toggler allows you to specify a delay for each of two tasks. It uses this delay to schedule the next task -- i.e., it will run task two if task one most recently ran, or vice versa. Further, if the toggle is re-invoked during the scheduling delay for a task, that scheduled task is canceled (state is unchanged).

Example: Spinner

To illustrate, let's revisit the spinner example from above:

var toggle = Toggler(
    /*taskOneDelay=*/250,
    /*taskTwoDelay=*/100
);

// (throttled) toggle on the spinner
toggle(showSpinner,hideSpinner);

// later, (throttled) toggle off the spinner
toggle(showSpinner,hideSpinner);

Here, the first toggle() call schedules the showSpinner() task to run in 250ms; if toggle() is called again before that has delay has transpired, the scheduled call to showSpinner() is canceled (and the spinner stays hidden).

Likewise, if the spinner is visible and toggle() is called, hideSpinner() is delayed by 100ms; if toggle() is called again before that delay has transpired, the scheduled call to hideSpinner() is canceled (and the spinner stays visible).

Toggling use-cases

The spinner example above is a common use-case for something like Toggler. But any UI control that can be toggled between two states is a potential candidate.

For example, you might use Toggler to asynchronously manage showing/hiding of hover/long-press tooltips, to avoid UX messy "quick flickering" of tooltips as a user moves their cursor or finger-touch around an interface. A brief delay on both show and hide will generally be friendlier for UX, requiring the user to pause over an element to express more obvious intent, etc. Similar goes for expanding menus/drop-downs.

Another reason to use Toggler would be to manage UI operations that involve animation (e.g., a sliding-in and sliding-out side drawer), since it can be very UX jarring for an animation to be interrupted when only partially complete. Toggler could for example ensure that once a show animation starts, it has a chance to gracefully finish before the element is hidden (either by animation or immediately).

Even more affirmative user events like clicks/taps -- e.g., opening a popup with a calendar or color picker -- can benefit UX with asynchronous toggling, because clicks/taps sometimes happen accidentally while users scroll around UI content.

Lag?

As touch interfaces became popular a decade or so ago, many mobile browsers introduced a ~300ms delay before firing click events on UI elements, because it was felt for UX reasons that distinguishing between a tap and a touch-and-drag (or other sophisticated gestures, like double-tap, pinch-to-zoom, etc) was important.

Unfortunately, for UIs (like games) where the tap is the main or only gesture, this across-the-board delay created a laggy feeling. Developers used multiple workarounds to avoid this delay, including CSS touch-action: manipulation and JS libraries like FastClick (now deprecated).

Luckily, modern browsers/devices are not necessarily applying these delays quite so universally, and there are more ways to handle these various cases and trade-offs.

Toggler is intended to be another tool in that effort. You can selectively re-introduce a brief delay (even shorter than 300ms) for a specific part of a UI. And, you can delay both the in and the out of a toggleable state -- something the other CSS/JS solutions just mentioned don't handle.

Deployment / Import

npm install @byojs/toggler

The @byojs/toggler npm package includes a dist/ directory with all files you need to deploy Toggler (and its dependencies) into your application/project.

Note: If you obtain this library via git instead of npm, you'll need to build dist/ manually before deployment.

Using a bundler

If you are using a bundler (Astro, Vite, Webpack, etc) for your web application, you should not need to manually copy any files from dist/.

Just import like so:

import Toggler from "@byojs/toggler";

The bundler tool should pick up and find whatever files (and dependencies) are needed.

Without using a bundler

If you are not using a bundler (Astro, Vite, Webpack, etc) for your web application, and just deploying the contents of dist/ as-is without changes (e.g., to /path/to/js-assets/toggler/), you'll need an Import Map in your app's HTML:

<script type="importmap">
{
    "imports": {
        "toggler": "/path/to/js-assets/toggler/toggler.mjs"
    }
}
</script>

Now, you'll be able to import the library in your app in a friendly/readable way:

import Toggler from "toggler";

Note: If you omit the above toggler import-map entry, you can still import Toggler by specifying the proper full path to the toggler.mjs file.

Toggler API

The API provided by Toggler is a single function -- the default export of the module.

This function receives two integer arguments, to initialize a toggler instance -- represented by another function as its return value -- to configure dual byojs/Scheduler instances. Internally, these two scheduler instances are wired to each other to asynchronously toggle a task between two states, by alternating calls of two functions.

import Toggler from "..";

var toggle = Toggler(
    /*taskOneDelay=*/250,
    /*taskTwoDelay=*/100
);

Toggling Tasks

To toggle between two tasks (function calls), pass them into the toggler instance (toggle() from above):

// (throttled) toggle on the spinner
toggle(showSpinner,hideSpinner);

// later, (throttled) toggle off the spinner
toggle(showSpinner,hideSpinner);

If the second toggle() call happens before the first interval has transpired (taskOneDelay configured above as 250ms), the first task (showSpinner()) will be canceled. However, if the second toggle() call doesn't happen before the first delay interval has transpired, the first task (showSpinner()) will complete successfully.

Either way, the second task (hideSpinner()) will then be scheduled (taskTwoDelay configured above as 100ms).

The toggling continues back-and-forth between the two tasks, with interval timer and cancelation, indefinitely, as long as the toggler instance (again, toggle() above) is always called with the same two functions.

You can share the same toggler instance can for toggling multiple pairs of tasks/functions, assuming the same timing settings should apply for each pair. However, do not have the same function instance participating in two or more pairs of toggling, as this will cause unexpected behavior.

Warning: The internal tracking of toggling task functions is based on function reference identity. If you pass an inline function expression (such as an => arrow), the function reference will be different each time, and will be treated as entirely separate functions -- thereby breaking the toggle tracking. Make sure to use the same stable function references pair for all toggling.

Re-building dist/*

If you need to rebuild the dist/* files for any reason, run:

# only needed one time
npm install

npm run build:all

Tests

This library only works in a browser, so its test suite must also be run in a browser.

Visit https://byojs.dev/toggler/ and click the "run tests" button.

Run Locally

To instead run the tests locally, first make sure you've already run the build, then:

npm test

This will start a static file webserver (no server logic), serving the interactive test page from http://localhost:8080/; visit this page in your browser and click the "run tests" button.

By default, the test/test.js file imports the code from the src/* directly. However, to test against the dist/* files (as included in the npm package), you can modify test/test.js, updating the /src in its import statements to /dist (see the import-map in test/index.html for more details).

License

All code and documentation are (c) 2024 Kyle Simpson and released under the MIT License. A copy of the MIT License is also included.