Creating simple comparative bars with JavaScript and CSS

Back a few months ago I reviewed the excellent SumAll service. One of the cooler parts of their service is a daily/weekly email summary of your stats. Here is a screen shot from my email this morning.

shot1

What I like about this are the simple bars between each number. They give you a real quick way to see your relative growth/drop from one day to the next. Like any good web developer, I was curious as to how they built this, so I right clicked, selected Inspect Element, and took a look at the code.

shot2

So - first off - there’s a lot of markup to make this work. That isn’t because the SumAll developers suck, it’s simply a matter of life when dealing with HTML email. But the base mechanism isn’t that difficult - a simple div with CSS. Obviously you could use one of the hundred or so different JS charting libraries out there, or Canvas, but why do all that when a bit of CSS is all you need.

I thought it would be interesting to try to replicate the look for a web page outside of email where I could use JavaScript to make it more dynamic. I began by creating a simple HTML page to represent a particular metric - the number of page views from last week and this week.

<!DOCTYPE html>
<html>
<head>
<meta charset="utf-8">
<title></title>
<meta name="description" content="">
<meta name="viewport" content="width=device-width">
</head>
<body>

<h2>Scores</h2>
<table>
	<tr>
		<th></th>
		<th>Last Week</th>
		<th></th>
		<th>This Week</th>
	</tr>
	<tr>
		<td>Page Views</td>
		<td><span id="pageviews_lw" data-raw="490121">490K</span></td>
		<td><span id="dobar"></span></td>
		<td><span id="pageviews_tw" data-raw="361902">362K</span></td>
	</tr>
</table>

</body>
</html>

There isn’t anything particularly special about this layout, but note that I’m using a formatted number (490K) versus the real number (490121). I wanted it to be simpler to read for the end user. However, I know I’m going to need the real number, so I embed it in the HTML using a data property. (Off topic aside - but I freaking love data attributes. So simple, so practical!)

You can view this version of the page here: http://www.raymondcamden.com/demos/2015/mar/19/test1.html. Before we go any further - please actually view that link. It isn’t pretty, but guess what? It works in every single browser known to humankind. Everything I do from now on will simply enhance the experience for people with JavaScript and more modern browsers. That’s something we should all consider when adding interactivity/fancy UI/etc to our pages! (And to be fair, I’m guilty of not doing proper progressive enhancement as well.)

Ok, so let’s build the next version. I began by modifying the dobar span to include a table to hold my bars. That may not be necessary, but I was mimicking what SumAll had built. I also included the CSS for each bar minus the portion that determined the height and the color. SumAll used black for the left side only, but I decided to use black for the 100% value and a different color for the other one. That just made more sense to me. This is the new HTML for the span:

<span id="dobar">

	<table><tr style="vertical-align:bottom">
		<td>
			<div style="margin-right:3px!important;width:4px;">&nbsp;</div>
		</td><td>
			<div style="margin-right:3px!important;width:4px;">&nbsp;</div>
		</td>
	</tr></table>
</span>

And now let’s look at the JavaScript.

var BIG_COLOR = "#000";
var SMALL_COLOR = "#3cb4e7";

$(document).ready(function() {
	
	//get our numbers
	var pv_lw = $("#pageviews_lw").data("raw");
	var pv_tw = $("#pageviews_tw").data("raw");
	
	var biggest = Math.max(pv_lw, pv_tw);
	var smallest = Math.min(pv_lw, pv_tw);
	//so what perc of biggest is smallest?
	
	var perc = Math.floor((smallest / biggest)*100);
	//so biggest uses 30, perc determines other
	var smallerBar = Math.floor((perc/100)*30);
	
	//do left side
	var css_lw, css_nw;
	if(pv_lw == biggest) {
		css_lw = "30px solid "+BIG_COLOR;
		css_nw = smallerBar+"px solid "+SMALL_COLOR;
	} else {
		css_nw = "30px solid "+BIG_COLOR;
		css_lw = smallerBar+"px solid "+SMALL_COLOR;		
	}

	$("span#dobar td:first-child div").css("border-top", css_lw);
	$("span#dobar td:last-child div").css("border-top", css_nw);

});

So really - it just comes down to math. Figure out the highest value, then the percentage difference for the other value. I used “30” to represent the highest bar so the other bar is a percentage of that. Then it is a simple matter of updating the CSS. Let me quickly thank Ian Devlin for his help finding a rookie mistake I made using jQuery.css. I had included a semicolon in the CSS value which totally broke the update. I’m sure I’ll never make that mistake again.

Here’s a screen shot of the result:

shot3

You can see this version in all its glory here: http://www.raymondcamden.com/demos/2015/mar/19/test2.html

So not rocket science, but nice I think. For the hell of it, and because I’m easily amused, I made a third version. I added some range fields to the bottom of the page:

<p>
Last Week: 0 <input type="range" min="0" max="200" value="99" id="leftRange"> 200<br/>
This Week: 0 <input type="range" min="0" max="200" value="32" id="rightRange"> 200<br/>
</p>

I was kinda surprised by how well these are supported now (CanIUse data) but as this version is just for fun, I don’t really care about what happens in older browsers. I then wrote a simple event listener for change on them and had them update the data when used.

var BIG_COLOR = "#000";
var SMALL_COLOR = "#3cb4e7";

function renderBar() {
	//get our numbers
	var pv_lw = $("#pageviews_lw").data("raw");
	var pv_tw = $("#pageviews_tw").data("raw");

	var biggest = Math.max(pv_lw, pv_tw);
	var smallest = Math.min(pv_lw, pv_tw);
	//so what perc of biggest is smallest?
	
	var perc = Math.floor((smallest / biggest)*100);
	//so biggest uses 30, perc determines other
	var smallerBar = Math.floor((perc/100)*30);
	
	var css_lw, css_nw;
	if(pv_lw == biggest) {
		css_lw = "30px solid "+BIG_COLOR;
		css_nw = smallerBar+"px solid "+SMALL_COLOR;
	} else {
		css_nw = "30px solid "+BIG_COLOR;
		css_lw = smallerBar+"px solid "+SMALL_COLOR;		
	}
	
	$("span#dobar td:first-child div").css("border-top", css_lw);
	$("span#dobar td:last-child div").css("border-top", css_nw);
};

$(document).ready(function() {

	renderBar();

	var $leftRange = $("#leftRange");
	var $rightRange = $("#rightRange");
	var $leftSpan = $("#pageviews_lw");
	var $rightSpan = $("#pageviews_tw");
	
	$("input[type=range]").on("input", function(e) {
		$leftSpan.text($leftRange.val());
		$leftSpan.data("raw", $leftRange.val());
		$rightSpan.text($rightRange.val());
		$rightSpan.data("raw", $rightRange.val());
		renderBar();
	});
	
});

You can then play around with the data and see the bars go up and down. Because… I don’t know. It’s fun.

shot4

You can test this version here: http://www.raymondcamden.com/demos/2015/mar/19/test3.html

Raymond Camden's Picture

About Raymond Camden

Raymond is a developer advocate looking for his next gig. He focuses on JavaScript, serverless and enterprise cat demos. If you like this article, please consider visiting my Amazon Wishlist or donating via PayPal to show your support.

Lafayette, LA https://www.raymondcamden.com

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