A smooth, responsive JavaScript plugin for collapsing and expanding long blocks of text with "Read more" and "Close" links.

The markup Readmore.js requires is so simple, you can probably use it with your existing HTML—there's no need for complicated sets of divs or hardcoded classes, just call new Readmore() on the element containing your block of text and Readmore.js takes care of the rest. Readmore.js works well on mobile and plays nicely with responsive designs, too.

Readmore.js has no external dependencies (no more jQuery—yay!) and works in all the "good" browsers, as well as IE10+; IE9 should work, but is not supported and the experience will not be ideal.

NOTE: This documentation is for the beta releases of the next version of Readmore.js.

Install Readmore.js with npm:

$ npm install readmore-js@next

Then include it in your HTML:

<script src="/node_modules/readmore-js/dist/readmore.js"></script>

Or, using Webpack or Browserify:

require('readmore-js');

new Readmore('article');

It's that simple. You can change the speed of the animation, the height of the collapsed block, and the open and close elements.

new Readmore('article', {
  speed: 75,
  lessLink: '<a href="#">Read less</a>'
});

• speed: 100 in milliseconds
• collapsedHeight: 200 in pixels
• heightMargin: 16 in pixels, avoids collapsing blocks that are only slightly larger than collapsedHeight
• moreLink: '<a href="#">Read more</a>' HTML string for the "more" toggle link; also accepts a callback function that returns an HTML string
• lessLink: '<a href="#">Close</a>' HTML string for the "less" toggle link; also accepts a callback function that returns an HTML string
• embedCSS: true insert required CSS dynamically, set this to false if you include the necessary CSS in a stylesheet
• blockCSS: 'display: block; width: 100%;' sets the styling of the blocks, ignored if embedCSS is false
• startOpen: false do not immediately truncate, start in the fully opened position
• sourceOrder: 'after' the toggle link is inserted 'before' or 'after' the block
• blockProcessed: function() {} called once per block during initilization after Readmore.js has processed the block
• beforeToggle: function() {} called after a more or less link is clicked, but before the block is collapsed or expanded
• afterToggle: function() {} called after the block is collapsed or expanded

If the element has a max-height CSS property, Readmore.js will use that value rather than the value of the collapsedHeight option.

You can pass a callback function instead of an HTML string for the moreLink and lessLink options. This is useful if you want alter the content of more/less toggle links on a per block basis. Your callback will receive the current block and must return a string.

Here's how you could use a callback to dynamically generate a moreLink containing the headline of a block.

new Readmore('article', {
  moreLink: function(element) {
    const headline = element.querySelector('h2').innerText;
    return `<a href="#">Read more about ${headline}</a>`;
  }
};

The beforeToggle and afterToggle callbacks both receive the same arguments: trigger, element, and expanded.

• trigger: the "Read more" or "Close" element that was clicked
• element: the block that is being collapsed or expanded
• expanded: Boolean; true means the block is expanded

The blockProcessed callback receives element and collapsible.

• element: the block that has just been processed
• collapsible: Boolean; false means the block was shorter than the specified minimum collapsedHeight--the block will not have a "Read more" link

Here's an example of how you could use the afterToggle callback to scroll back to the top of a block when the "Close" link is clicked.

new Readmore('article', {
  afterToggle: function(trigger, element, expanded) {
    if(!expanded) { // The "Close" link was clicked
      window.scrollTo({ top: element.offsetTop, behavior: 'smooth' });
    }
  }
});

If beforeToggle returns false the toggle action is halted and afterToggle will not be executed. This is useful if you want prevent a toggle based on some application logic--the state of another element on the page, current phase of the moon, etc.

The Readmore class constructor and all methods accept as arguments, either:

• selector String valid CSS selectors; e.g. 'blockquote', '.truncate-block', or '#blog .section'
• Element a single Element object; e.g. return value of document.getElementById('blog')
• NodeList a NodeList collection of Elements; e.g. return value of document.querySelectorAll('article')

new Readmore(selector String | Element | NodeList);

Toggle a block programmatically.

// As instance method
rmjs.toggle(selector String | Element | NodeList);

You can toggle a block from code:

// Store a reference to an instance of Readmore
var rmjs = new Readmore('article');
rmjs.toggle('article:first-child')

Remove Readmore.js functionality from specific blocks or all blocks.

rmjs.destroy(null | selector String | Element | NodeList);

When invoked with null, will remove Readmore.js functionality from all of the instance's blocks.

You can remove the Readmore.js functionality like so:

// Store a reference to an instance of Readmore
var rmjs = new Readmore('article');
// Now call destroy on the instance
rmjs.destroy();

Or, you can be more surgical by specifying a particular element:

// Store a reference to an instance of Readmore
var rmjs = new Readmore('article');
// Now remove Readmore from just the first block
rmjs.destroy(document.querySelector('article:first-child'));
// or
rmjs.destroy('article:nth-of-type(2)');

Readmore.js is designed to use CSS for as much functionality as possible: collapsed height can be set in CSS with the max-height property; "collapsing" is achieved by setting overflow: hidden on the containing block and changing the height property; and, finally, the expanding/collapsing animation is done with CSS3 transitions.

By default, Readmore.js inserts the following CSS, in addition to some transition-related rules:

selector + [data-readmore-toggle], selector[data-readmore] {
  display: block;
  width: 100%;
}

selector would be the element you invoked readmore() on, e.g.: new Readmore('selector')

You can override the base rules when you set up Readmore.js like so:

new Readmore('article', { blockCSS: 'display: inline-block; width: 50%;' });

If you want to include the necessary styling in your site's stylesheet, you can disable the dynamic embedding by setting embedCSS to false:

new Readmore('article', { embedCSS: false });

If you wanted to set a maxHeight based on lines, you could do so in CSS with something like:

body {
  font: 16px/1.5 sans-serif;
}
/* Show only 4 lines in smaller screens */
article {
  max-height: 6em; /* (4 * 1.5 = 6) */
}

Then, with a media query you could change the number of lines shown, like so:

/* Show 8 lines on larger screens */
@media screen and (min-width: 640px) {
  article {
    max-height: 12em;
  }
}

Pull requests are always welcome, but not all suggested features will get merged. Feel free to contact me if you have an idea for a feature.

Pull requests should include the minified script and this readme and the demo HTML should be updated with descriptions of your new feature.

You'll need NPM:

$ npm install

Which will install the necessary development dependencies. Then, to build the minified script:

$ npm run build