Readmore JS

Lightweight, framework-agnostic plugin to clamp text to N lines (or a fixed pixel height) with an ellipsis and a Read more / Read less toggle button.

• Zero dependencies, ~1 KB
• TypeScript types included
• CSS-driven clamping via -webkit-line-clamp or max-height
• The toggle button is only created when the text actually overflows

Installation

npm install @frontfactory/readmore

Playground

Try it live on StackBlitz — no installation required:

Or run it locally:

npm run dev

Usage

import { ReadMore } from '@frontfactory/readmore';
import '@frontfactory/readmore/style.css';

// clamp to 3 lines
ReadMore.init('.excerpt', {
    lines: 3
});

// clamp to a fixed pixel height
ReadMore.init('.excerpt', {
    height: 80
});

Or instantiate against a single element:

const el = document.querySelector<HTMLElement>('#bio');

if (el) new ReadMore(el, {
    lines: 4
});

Options

Option	Type	Default	Description
lines	number	3	Number of lines to clamp to. Ignored if height is set.
height	number	—	Max height in pixels. Takes precedence over lines when provided.
moreText	string	'Read more'	Label of the button when the text is collapsed.
lessText	string	'Read less'	Label of the button when the text is expanded.
buttonClass	string	'readmore-btn'	Class applied to the toggle button.
expandedClass	string	'is-expanded'	Class applied to the target element while expanded.
openingClass	string	'is-opening'	Transient class applied while expanding, removed after transition.
closingClass	string	'is-closing'	Transient class applied while collapsing, removed after transition.

API

const instance = new ReadMore(element, options);

instance.toggle();      // expand / collapse programmatically
instance.expanded;      // boolean getter
instance.destroy();     // remove button, classes and listeners

ReadMore.init(selector, options); // returns ReadMore[]

How it works

The plugin sets a CSS custom property on the target element and toggles .readmore-clamp. In lines mode (default), it sets --readmore-lines and the bundled stylesheet applies -webkit-line-clamp, producing an ellipsis at the end of the last visible line. In height mode (height option), it sets --readmore-height and applies max-height via the .readmore-clamp--height modifier class instead. The toggle button is mounted right after the element only when the content actually overflows, and unmounted again on resize if the text ends up fitting.

Transient classes for animations

In addition to expandedClass (which stays applied for the entire expanded state), the plugin applies short-lived openingClass and closingClass markers on the target element at the moment of expand and collapse respectively. Each is added when the toggle starts and removed automatically once the CSS transition on the element ends — or on the next tick if no transition is declared. Use them as hooks to drive enter/leave animations:

.is-opening { 
    /* expand animation */
}

.is-closing {
    /* collapse animation */ 
}