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Collapse

A collapse component for expandable sections, progressive disclosure and accordion-style content.

Import
the javascript logo
import { Collapse } from "@schukai/monster/source/components/layout/collapse.mjs";
Source
the git logo
Package
the npm logo
Since
3.74.0
State: closed
Collapse is useful for optional details, FAQ answers, or secondary notes that should stay out of the way.

Introduction

The Monster Collapse component hides secondary content until it is needed. Use it for progressive disclosure when a section should stay available but not always expanded.

When to use Collapse

  • Use it for optional details: Advanced filters, extra explanations and secondary settings fit well.
  • Use it to shorten long pages: Users can open only the parts that matter to them.
  • Do not hide primary information by default: Content required to complete the main task should usually stay visible.

Typical mistakes

Make the collapsed heading informative. Users should know what becomes available before they open the section.

Collapse Simple

This example shows how a basic collapse works. It is important to note that the collapse itself does not have an open button. Therefore, you have to add your own button or other functionality for this purpose.

State: closed
Delivery notes

Keep less-frequent details collapsed by default and reveal them through the public API instead of inline event handlers.

Javascript

import "@schukai/monster/source/components/layout/collapse.mjs";

const collapse = document.getElementById("collapse-simple");
const log = document.getElementById("collapse-simple-log");

document.getElementById("collapse-simple-toggle")?.addEventListener("click", () => {
	collapse?.toggle();
});

document.getElementById("collapse-simple-open")?.addEventListener("click", () => {
	collapse?.open();
});

document.getElementById("collapse-simple-close")?.addEventListener("click", () => {
	collapse?.close();
});

collapse?.addEventListener("monster-collapse-before-open", () => {
	log.textContent = "State: opening";
});

collapse?.addEventListener("monster-collapse-open", () => {
	log.textContent = "State: open";
});

collapse?.addEventListener("monster-collapse-before-close", () => {
	log.textContent = "State: closing";
});

collapse?.addEventListener("monster-collapse-closed", () => {
	log.textContent = "State: closed";
});

HTML

<section style="display:grid;gap:var(--monster-space-4);">
  <div style="display:flex;gap:var(--monster-space-3);flex-wrap:wrap;align-items:center;">
    <button id="collapse-simple-toggle" type="button">Toggle details</button>
    <button id="collapse-simple-open" type="button">Open</button>
    <button id="collapse-simple-close" type="button">Close</button>
    <span id="collapse-simple-log">State: closed</span>
  </div>

  <monster-collapse id="collapse-simple">
    <div style="display:grid;gap:var(--monster-space-3);padding:var(--monster-space-4);background:var(--monster-bg-color-primary-2);color:var(--monster-color-primary-2);border:1px solid var(--monster-color-border-primary-2);">
      <strong>Delivery notes</strong>
      <p style="margin:0;">
        Keep less-frequent details collapsed by default and reveal them through the
        public API instead of inline event handlers.
      </p>
    </div>
  </monster-collapse>
</section>

Stylesheet

/** no additional stylesheet is defined **/
Open in playground

Collapse With Events

This variant highlights the event lifecycle. It is useful when outer UI should react to the collapsed state without touching component internals.

FAQ style section Waiting for user interaction
Yes. The collapse emits lifecycle events that can be mirrored into surrounding status UI or analytics hooks.

Javascript

import "@schukai/monster/source/components/layout/collapse.mjs";

const collapse = document.getElementById("collapse-events-demo");
const log = document.getElementById("collapse-events-log");

document.getElementById("collapse-events-toggle")?.addEventListener("click", () => {
	collapse?.toggle();
});

collapse?.addEventListener("monster-collapse-before-open", () => {
	log.textContent = "Lifecycle: before open";
});

collapse?.addEventListener("monster-collapse-open", () => {
	log.textContent = "Lifecycle: open";
});

collapse?.addEventListener("monster-collapse-before-close", () => {
	log.textContent = "Lifecycle: before close";
});

collapse?.addEventListener("monster-collapse-closed", () => {
	log.textContent = "Lifecycle: closed";
});

HTML

<section style="display:grid;gap:var(--monster-space-4);">
  <div style="display:grid;gap:var(--monster-space-2);padding:var(--monster-space-4);background:var(--monster-bg-color-secondary-2);color:var(--monster-color-secondary-2);border:1px solid var(--monster-color-border-secondary-2);">
    <strong>FAQ style section</strong>
    <span id="collapse-events-log">Waiting for user interaction</span>
  </div>

  <button id="collapse-events-toggle" type="button">Toggle answer</button>

  <monster-collapse id="collapse-events-demo">
    <div style="padding:var(--monster-space-4);background:var(--monster-bg-color-primary-1);color:var(--monster-color-primary-1);border:1px solid var(--monster-color-border-primary-2);">
      Yes. The collapse emits lifecycle events that can be mirrored into surrounding
      status UI or analytics hooks.
    </div>
  </monster-collapse>
</section>

Stylesheet

/** no additional stylesheet is defined **/
Open in playground

Component Design

The Monster Collapse component uses the Shadow DOM to encapsulate its structure and styles. It provides an expandable and collapsible container for displaying content. The design ensures that the internal behavior and appearance of the component remain consistent and unaffected by external scripts or styles.

Shadow DOM and Accessibility

By leveraging the Shadow DOM, the Monster Collapse component isolates its internal elements. Accessibility is a key consideration, with support for ARIA roles and events to provide compatibility with screen readers and assistive technologies. The component ensures that users can interact with the collapse content seamlessly using both mouse and keyboard inputs.

Customizing Through Exported Parts

The Monster Collapse component exposes specific exported parts to allow developers to customize the appearance of the collapse container, decorative elements, and content while preserving encapsulation.

Available Part Attributes

  • control: Represents the entire control container, including the toggle behavior.
  • container: Targets the content area of the collapse.
  • deco: Refers to the decorative line or element added for visual separation.

Below is an example of how to style the collapse component using the CSS part selector:


monster-collapse::part(control) {
    background-color: #f5f5f5;
    border-radius: 6px;
    transition: box-shadow 0.3s ease;
}

monster-collapse::part(container) {
    padding: 16px;
    font-size: 1rem;
    line-height: 1.5;
    color: #333;
}

monster-collapse::part(deco) {
    height: 2px;
    background-color: #007bff;
    margin-top: 8px;
}

Explanation of the Example

  • monster-collapse::part(control): Styles the entire collapse control container with a background and hover effect.
  • monster-collapse::part(container): Adds padding and styles the content within the collapse area.
  • monster-collapse::part(deco): Customizes the decorative line with a blue background color and spacing.

Accessibility

The Monster Collapse component is designed to be fully accessible. It includes:

  • Keyboard Navigation: Users can expand or collapse the content using keyboard inputs.
  • ARIA Roles: ARIA roles are applied to indicate the state (open or closed) of the collapse content.
  • Focus Management: Focus is maintained on the relevant interactive elements during toggling.

These features ensure that the component delivers a smooth and inclusive experience for all users, including those relying on assistive technologies.

HTML Structure

<monster-collapse></monster-collapse>

JavaScript Initialization

const element = document.createElement('monster-collapse');
document.body.appendChild(element);

Exported

Collapse, nameSymbol

Derived from

CustomElement

Options

The Options listed in this section are defined directly within the class. This class is derived from several parent classes, including the CustomElement class. Therefore, it inherits Options from these parent classes. If you cannot find a specific Options in this list, we recommend consulting the documentation of the CustomElement.

Option
Type
Default
Description
templates
object
Template definitions
templates.main
string
undefined
Main template
classes
object
CSS classes
classes.container
string
padding
CSS class for the container
features
object
Feature configuration
features.accordion
boolean
true
Enable accordion mode
features.persistState
boolean
true
Enable persist state (Host and Config-Manager required)
features.useScrollValues
boolean
false
Use scroll values (scrollHeight) instead of clientHeight for the height calculation
openByDefault
boolean
false
Open the details by default

  • since
  • deprecated

Properties and Attributes

The Properties and Attributes listed in this section are defined directly within the class. This class is derived from several parent classes, including the CustomElement class and ultimately from HTMLElement. Therefore, it inherits Properties and Attributes from these parent classes. If you cannot find a specific Properties and Attributes in this list, we recommend consulting the documentation of the CustomElement.

  • data-monster-options: Sets the configuration options for the collapse component when used as an HTML attribute.
  • data-monster-option-[name]: Sets the value of the configuration option [name] for the collapse component when used as an HTML attribute.

Methods

The methods listed in this section are defined directly within the class. This class is derived from several parent classes, including the CustomElement class and ultimately from HTMLElement. Therefore, it inherits methods from these parent classes. If you cannot find a specific method in this list, we recommend consulting the documentation of the CustomElement.

Constructor

constructor()

Behavioral methods

adjustHeight()
Returns
  • {Collapse}
Events
  • monster-collapse-adjust-height This event is fired when the height is adjusted. As a detail, the height is passed.
This method is called when the element is inserted into a document, including into a shadow tree.
close()
Returns
  • {Collapse}
Events
  • monster-collapse-before-close This event is fired before the collapse is closed.
  • monster-collapse-closed This event is fired after the collapse is closed.
Close the collapse
open()
Returns
  • {Collapse}
Events
  • monster-collapse-before-open This event is fired before the collapse is opened.
  • monster-collapse-open This event is fired after the collapse is opened.
Open the collapse
toggle()
Returns
  • {Collapse}

State query methods

isClosed()
Returns
  • {boolean}
isOpen()
Returns
  • {boolean}

Static methods

[instanceSymbol]()
Returns
  • {symbol}
This method is called by the instanceof operator.
getCSSStyleSheet()
Returns
  • {CSSStyleSheet[]}
getTag()
Returns
  • {string}

Lifecycle methods

Lifecycle methods are called by the environment and are usually not intended to be called directly.

[assembleMethodSymbol]()
Returns
  • {void}
connectedCallback()
Returns
  • {void}
disconnectedCallback()
Returns
  • {void}

Events

The component emits the following events:

  • monster-collapse-before-open
    This event is fired before the collapse is opened.
  • monster-collapse-open
    This event is fired after the collapse is opened.
  • monster-collapse-before-close
    This event is fired before the collapse is closed.
  • monster-collapse-closed
    This event is fired after the collapse is closed.
  • monster-collapse-adjust-height
    This event is fired when the height is adjusted. As a detail, the height is passed.

For more information on how to handle events, see the mdn documentation.

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