Prism Line Number Plugin

By  on  

The Mozilla Developer Network (MDN) is in the midst of a remodel (sorry for the spoiler) and we've been implementing features incrementally.  One larger front-end change we'll be implementing is using the PrismJS for document code syntax highlighting.  One requirement of MDN's syntax highlighter is that line numbers are displayed, a functionality not provided by Prism.  Prism does provide a line-highlighting plugin but not a line-numbering plugin, so I used that plugin as my base and simply simplified it to provide numbers for a lines.

The CSS

The CSS here is copied from the line-highlighting plugin.  I've changed the attribute to data-number, which we'll use instead of data-line, and I've changed the colors used for the line background:

pre[data-number] {
	position: relative;
	padding: 1em 0 1em 3em;
}

.line-number {
	position: absolute;
	left: 0;
	right: 0;
	padding: inherit 0;
	margin-top: 1em; /* Same as .prism's padding-top */

	background: transparent;
	
	pointer-events: none;
	
	line-height: inherit;
	white-space: pre;
}

	.line-number:before,
	.line-number[data-end]:after {
		content: attr(data-start);
		position: absolute;
		top: .4em;
		left: .6em;
		min-width: 1em;
		padding: 0 .5em;
		color: #999;
		font: bold 65%/1.5 sans-serif;
		text-align: center;
		vertical-align: .3em;
		border-radius: 999px;
		text-shadow: none;
		border: 0;
	}
	
	.line-number[data-end]:after {
		content: attr(data-end);
		top: auto;
		bottom: .4em;
	}

Of course you can style the line number element to however you'd like, but this CSS keeps styles fairly consistent with the line-highlighting plugin.

The JavaScript

Here's the JavaScript portion for the plugin in all its glory:

/*
	This plugins was created based on the Prism line-numbering plugin.
	This plugin aims to number all lines and is independent of highlighting.
*/
(function(){

if(!window.Prism || !document.querySelectorAll) {
	return;
}

function $$(expr, con) {
	return Array.prototype.slice.call((con || document).querySelectorAll(expr));
}
    
function numberLines(pre) {
	var offset = +pre.getAttribute('data-line-offset') || 0;
	var lineHeight = parseFloat(getComputedStyle(pre).lineHeight);
	var code = pre.querySelector('code');
	var numLines = code.innerHTML.split('\n').length;
	pre.setAttribute('data-number', '');

	for (var i=1; i <= numLines; i++) {
		var line = document.createElement('div');
		line.className = 'line-number';
		line.setAttribute('data-start', i);
		line.style.top = (i - offset - 1) * lineHeight + 'px';
		
		(code || pre).appendChild(line);
	}
}

Prism.hooks.add('after-highlight', function(env) {
	var pre = env.element.parentNode;
	
	if (!pre || !/pre/i.test(pre.nodeName)) {
		return;
	}

	$$('.line-number', pre).forEach(function (line) {
		line.parentNode.removeChild(line);
	});
	
	numberLines(pre);
});

})();

This code is also based on the syntax-highlighting plugin's code, but much more simplified because there's less line-numbering logic.

If there's enough interest in what I have, I can make a GitHub repo for the plugin.  I haven't to this point because I believe this plugin could/should be merged with the line-highlighting plugin, since in many cases, developers reference line numbers.  In any event, this plugin may be what you're looking for.  Let me know if you have updates or ideas!

Recent Features

  • By
    Send Text Messages with PHP

    Kids these days, I tell ya.  All they care about is the technology.  The video games.  The bottled water.  Oh, and the texting, always the texting.  Back in my day, all we had was...OK, I had all of these things too.  But I still don't get...

  • By
    LightFace:  Facebook Lightbox for MooTools

    One of the web components I've always loved has been Facebook's modal dialog.  This "lightbox" isn't like others:  no dark overlay, no obnoxious animating to size, and it doesn't try to do "too much."  With Facebook's dialog in mind, I've created LightFace:  a Facebook lightbox...

Incredible Demos

  • By
    MooTools Overlay Plugin

    Overlays have become a big part of modern websites; we can probably attribute that to the numerous lightboxes that use them. I've found a ton of overlay code snippets out there but none of them satisfy my taste in code. Many of them are...

  • By
    TextboxList for MooTools and jQuery by Guillermo Rauch

    I'll be honest with you: I still haven't figured out if I like my MooTools teammate Guillermo Rauch. He's got a lot stacked up against him. He's from Argentina so I get IM'ed about 10 times a day about how great Lionel...

Discussion

  1. Jonas

    This fails in WebKit, as getComputedStyle(pre).lineHeight returns ‘normal’.
    See also: https://github.com/LeaVerou/dabblet/pull/175

    • Ahh yes Jonas; I encountered that issue and explicitly set a line-height within a different stylesheet so as to avoid this issue.

  2. Maybe you missed it, but PrismJS does have a line numbering plugin. More info can be found on http://prismjs.com/plugins/line-numbers/

    • Hmm, that may be new. Thanks Mark!

    • So I just took a look at this and the line-numbers plugin isn’t compatible with the line-highlight plugin; mine is.

Wrap your code in <pre class="{language}"></pre> tags, link to a GitHub gist, JSFiddle fiddle, or CodePen pen to embed!