It’s the first thing your eyes look for when you’re switching tabs.

That’s one way of explaining what a favicon is. The tab area is a much more precious screen real-estate than what most assume. If done right, besides being a label with icon, it can be the perfect billboard to represent what’s in or what’s happening on a web page.

The CSS-Tricks Favicon

Favicons are actually at their most useful when you’re not active on a tab. Here’s an example:

Imagine you’re backing up photos from your recent summer vacation to a cloud service. While they are uploading, you’ve opened a new tab to gather details about the places you went on vacation to later annotate those photos. One thing led to the other, and now you’re watching Casey Neistat on the seventh tab. But you can’t continue your YouTube marathon without the anxious intervals of checking back on the cloud service page to see if the photos have been uploaded.

It’s this type of situation where we can get creative! What if we could dynamically change the pixels in that favicon and display the upload progress? That’s exactly what we’ll do in this article.

In supported browsers, we can display a loading/progress animation as a favicon with the help of JavaScript, HTML <canvas> and some centuries-old geometry.

Jumping straight in, we’ll start with the easiest part: adding the icon and canvas elements to the HTML.

<head> <link rel="icon" type="image/png" href="" width=32px> </head> <body> <canvas width=32 height=32></canvas> </body>

In practical use, you would want to hide the <canvas> on the page, and one way of doing that is with the HTML hidden attribute.

<canvas hidden width=32 height=32></canvas>

I’m going to leave the <canvas> visible on the page for you to see both the favicon and canvas images animate together.

Both the favicon and the canvas are given a standard favicon size: 32 square pixels.

For demo purposes, in order to trigger the loading animation, I’m adding a button to the page which will start the animation when clicked. This also goes in the HTML:

<button>Load</button>

Now let’s set up the JavaScript. First, a check for canvas support:

onload = ()=> { canvas = document.querySelector('canvas'), context = canvas.getContext('2d'); if (!!context) { /* if canvas is supported */ } };

Next, adding the button click event handler that will prompt the animation in the canvas.

button = document.querySelector('button'); button.addEventListener('click', function() { /* A variable to track the drawing intervals */ n = 0, /* Interval speed for the animation */ loadingInterval = setInterval(drawLoader, 60); });

drawLoader will be the function doing the drawing at intervals of 60 milliseconds each, but before we code it, I want to define the style of the lines of the square to be drawn. Let’s do a gradient.

/* Style of the lines of the square that'll be drawn */ let gradient = context.createLinearGradient(0, 0, 32, 32); gradient.addColorStop(0, '#c7f0fe'); gradient.addColorStop(1, '#56d3c9'); context.strokeStyle = gradient; context.lineWidth = 8;

In drawLoader , we’ll draw the lines percent-wise: during the first 25 intervals, the top line will be incrementally drawn; in second quarter, the right line will be drawn; and so forth.

The animation effect is achieved by erasing the <canvas> in each interval before redrawing the line(s) from previous interval a little longer.

During each interval, once the drawing is done in the canvas, it’s quickly translated to a PNG image to be assigned as the favicon.

function drawLoader() { with(context) { clearRect(0, 0, 32, 32); beginPath(); /* Up to 25% */ if (n<=25){ /* (0,0)-----(32,0) */ // code to draw the top line, incrementally } /* Between 25 to 50 percent */ else if(n>25 && n<=50){ /* (0,0)-----(32,0) | | (32,32) */ // code to draw the top and right lines. } /* Between 50 to 75 percent */ else if(n>50 && n<= 75){ /* (0,0)-----(32,0) | | (0,32)----(32,32) */ // code to draw the top, right and bottom lines. } /* Between 75 to 100 percent */ else if(n>75 && n<=100){ /* (0,0)-----(32,0) | | | | (0,32)----(32,32) */ // code to draw all four lines of the square. } stroke(); } // Convert the Canvas drawing to PNG and assign it to the favicon favicon.href = canvas.toDataURL('image/png'); /* When finished drawing */ if (n === 100) { clearInterval(loadingInterval); return; } // Increment the variable used to keep track of the drawing intervals n++; }

Now to the math and the code for drawing the lines.

Here’s how we incrementally draw the top line at each interval during the first 25 intervals:

n = current interval, x = x-coordinate of the line’s end point at a given interval. (y-coordinate of the end point is 0 and start point of the line is 0,0)

At the completion of all 25 intervals, the value of x is 32 (the size of the favicon and canvas.)

So…

x/n = 32/25 x = (32/25) * n

The code to apply this math and draw the line is:

moveTo(0, 0); lineTo((32/25)*n, 0);

For the next 25 intervals (right line), we target the y coordinate similarly.

moveTo(0, 0); lineTo(32, 0); moveTo(32, 0); lineTo(32, (32/25)*(n-25));

And here’s the instruction to draw all four of the lines with the rest of the code.

function drawLoader() { with(context) { clearRect(0, 0, 32, 32); beginPath(); /* Up to 25% of the time assigned to draw */ if (n<=25){ /* (0,0)-----(32,0) */ moveTo(0, 0); lineTo((32/25)*n, 0); } /* Between 25 to 50 percent */ else if(n>25 && n<=50){ /* (0,0)-----(32,0) | | (32,32) */ moveTo(0, 0); lineTo(32, 0); moveTo(32, 0); lineTo(32, (32/25)*(n-25)); } /* Between 50 to 75 percent */ else if(n>50 && n<= 75){ /* (0,0)-----(32,0) | | (0,32)----(32,32) */ moveTo(0, 0); lineTo(32, 0); moveTo(32, 0); lineTo(32, 32); moveTo(32, 32); lineTo(-((32/25)*(n-75)), 32); } /* Between 75 to 100 percent */ else if(n>75 && n<=100){ /* (0,0)-----(32,0) | | | | (0,32)----(32,32) */ moveTo(0, 0); lineTo(32, 0); moveTo(32, 0); lineTo(32, 32); moveTo(32, 32); lineTo(0, 32); moveTo(0, 32); lineTo(0, -((32/25)*(n-100))); } stroke(); } // Convert the Canvas drawing to PNG and assign it to the favicon favicon.href = canvas.toDataURL('image/png'); /* When finished drawing */ if (n === 100) { clearInterval(loadingInterval); return; } // Increment the variable used to keep track of drawing intervals n++; }

That’s all! You can see and download the demo code from this GitHub repo. Bonus: if you’re looking for a circular loader, check out this repo.