@botandrose/progress-bar

v0.6.1

Published

5 days ago

A linnear and circular progress bar web component

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1,378

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mgeisel

progress-bar web-component custom-element

progress-bar

A minimal progress bar web component.

Usage

Via Script Tag

<!DOCTYPE html>
<html>
<head>
  <script type="module" src="https://cdn.jsdelivr.net/npm/@botandrose/[email protected]/+esm"></script>
</head>
<body>
  <progress-bar percent="50">
    <a href="/download" download>file.pdf</a>
  </progress-bar>
</body>
</html>

Via ES Module Import

import ProgressBar from '@botandrose/progress-bar';

// Component auto-registers as <progress-bar>
const bar = document.querySelector('progress-bar');
bar.percent = 75;

API

Properties

percent (number | null) - The progress percentage. Numeric values are clamped to 0-100; a non-numeric value throws. When unset — no percent attribute, or percent = null — the bar is indeterminate: the fill animates as a sweeping segment (a spinning arc in circular mode) and aria-valuenow is dropped, the standard signal for an indeterminate progressbar. Set a number to make it determinate. Default: indeterminate. Can be set as attribute or property.
error (boolean) - Whether the bar is in an error state. In linear mode this recolors the fill to --error-color; in circular mode it drops the arc and renders a static full ring plus a centered X in --error-color — a "failed" glyph. Reflected between the error property and the error attribute, so <progress-bar error> and el.error = true are equivalent. Default: false.
rate (number | null) - Optimistic auto-advance, in percent per second. When set on a determinate bar, the component creeps percent forward on its own at 30Hz (so rate = 30 adds ~1% every tick) — useful when you expect steady progress but only receive occasional real updates. Negative rates drain the bar. On reaching the bound it's heading toward (100, or 0 for a negative rate) it clears its own rate; a later percent change re-arms it. An indeterminate bar (no percent) ignores rate entirely. Non-numeric values throw. Reflected between property and rate attribute. Default: unset (no auto-advance).
indeterminate (boolean, read-only) - Whether the bar is indeterminate, i.e. whether percent is unset. There is no indeterminate attribute — drive it through percent (omit it, or set the property to null).
mode (string) - "linear" (default) renders the horizontal fill bar; "circular" renders an SVG ring whose arc tracks percent, with the slotted content centered. Both modes honor error and the indeterminate (no-percent) state.

<progress-bar>working…</progress-bar>              <!-- indeterminate: no percent -->
<progress-bar percent="50">file.pdf</progress-bar>
<progress-bar percent="0" rate="20">file.pdf</progress-bar>  <!-- creeps forward at 20%/s -->
<progress-bar mode="circular" percent="42">42%</progress-bar>
<progress-bar mode="circular"></progress-bar>      <!-- indeterminate -->

Slots

Default slot - Content displayed over the progress bar (e.g., filename, download link)

Styling

Host-level appearance is plain CSS — style the element directly:

progress-bar {
  background: #333;          /* unfilled track */
  border: 1px solid #999;
  border-radius: 4px;        /* the fill is clipped to match */
}

Custom properties are reserved for the sealed shadow internals that CSS can't otherwise reach:

progress-bar {
  --progress-color: rgb(57, 137, 39); /* fill color */
  --error-color: #7a242f;             /* fill color when the element has the [error] attribute */
  --indeterminate-color: #999;        /* fill / arc color while indeterminate */
  --progress-duration: 120ms;         /* fill / dashoffset transition */
  --bar-height: 32px;                 /* minimum bar height (linear) */
  --bar-padding: 8px;                 /* padding around the label (linear) */
  --track-color: #333333;             /* unfilled ring color (circular) */
  --indeterminate-duration: 1.5s;     /* sweep / spin animation period */
  --circular-size: 64px;              /* ring diameter (circular) */
  --circular-thickness: 16;           /* ring stroke width (circular); radius auto-fits any value */
}

Accessibility

The element exposes role="progressbar" with aria-valuemin, aria-valuemax, and a live aria-valuenow.

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