As I continue to dig into Leaflet, I was recently asked about custom markers based on data, so for example, some locations for a store may use one icon while others use another. I did some digging, and while it turns out Leaflet has deep support for customizing markers, it does take a little bit of work. Here's what I found.

First off, this is the default marker:

Out of the box, this is it. Period. I can appreciate the library wanting to keep its size to a minimum, but I was a bit surprised. That being said, the library provides really flexible support for creating your own markers. The first thing I found was the tutorial, Markers With Custom Icons. In this tutorial, they describe the process of creating an instance of the icon class and specifying resources for the icon and shadow. Technically, this looked incredibly simple, and again, flexible, but the immediate issue I ran into was... ok, where do I find more icons?

I did some more digging and came across this open-source project, leaflet-color-markers, which provides a set of markers in the same style as the original, but in a variety of colors. Their read.me demonstrates the usage like so:

var greenIcon = new L.Icon({
  iconUrl: 'https://raw.githubusercontent.com/pointhi/leaflet-color-markers/master/img/marker-icon-2x-green.png',
  shadowUrl: 'https://cdnjs.cloudflare.com/ajax/libs/leaflet/0.7.7/images/marker-shadow.png',
  iconSize: [25, 41],
  iconAnchor: [12, 41],
  popupAnchor: [1, -34],
  shadowSize: [41, 41]
});

L.marker([51.5, -0.09], {icon: greenIcon}).addTo(map);

Now... I'm hesitant to suggest making use of raw.githubusercontent.com, as I've always heard that it wasn't meant to be used in production applications. That being said, for today I will, and keep in mind that you can take the asset (for example, marker-icon-2x-green.png) and download it to your website.

I tested this myself and it worked fine, but I wanted the smaller size icons, not the one demonstrated above. I simply copied the URL (https://raw.githubusercontent.com/pointhi/leaflet-color-markers/master/img/marker-icon-green.png), but then the four size/anchor properties stopped working well.

That made sense - I mean, I had a different size icon, and my first thought was, well, I'll just keep tweaking numbers till I get it right, but then I went back to the Leaflet docs, specifically for Icon, and noticed this part:

In order to customize the default icon, just change the properties of L.Icon.Default.prototype.options (which is a set of Icon options).

On a whim, I simply entered L.Icon.Default.prototype.options in my console, and got the following:

{
  "iconUrl": "marker-icon.png",
  "iconRetinaUrl": "marker-icon-2x.png",
  "shadowUrl": "marker-shadow.png",
  "iconSize": [
    25,
    41
 ],
  "iconAnchor": [
    12,
    41
 ],
  "popupAnchor": [
    1,
    -34
 ],
  "tooltipAnchor": [
    16,
    -28
 ],
  "shadowSize": [
    41,
    41
 ]
}

Woot. So with these defaults, I was able to figure out how to combine that project's custom colors with the 'regular' size markers and set the right values.

I'm not quite done yet. One more cool aspect of the Leaflet tutorial on custom markers was how they demonstrated that you could define your own custom icon class, and then make new instances with only slight tweaks. This is taken right from their tutorial:

var LeafIcon = L.Icon.extend({
    options: {
        shadowUrl: 'leaf-shadow.png',
        iconSize: [38, 95],
        shadowSize: [50, 64],
        iconAnchor: [22, 94],
        shadowAnchor: [4, 62],
        popupAnchor: [-3, -76]
 }
});


var greenIcon = new LeafIcon({iconUrl: 'leaf-green.png'}),
    redIcon = new LeafIcon({iconUrl: 'leaf-red.png'}),
    orangeIcon = new LeafIcon({iconUrl: 'leaf-orange.png'});

I took this approach, and merged it with the icons from the GitHub project, and came up with this snippet:

let ColorIcon =  L.Icon.extend({
    options: {
        shadowUrl: 'https://cdnjs.cloudflare.com/ajax/libs/leaflet/1.9.4/images/marker-shadow.png',
        iconSize: [25, 41],
        shadowSize: [41, 41],
        iconAnchor: [12, 41],
        popupAnchor: [1, -34]
 }
});

let greenIcon = new ColorIcon({iconUrl: 'https://raw.githubusercontent.com/pointhi/leaflet-color-markers/master/img/marker-icon-green.png'});

let redIcon = new ColorIcon({iconUrl: 'https://raw.githubusercontent.com/pointhi/leaflet-color-markers/master/img/marker-icon-red.png'});

Here is an example using it:

L.marker([30.471165, -91.147385], 
 {icon: greenIcon}).addTo(map).bindPopup("Baton Rouge");

This was all maybe twenty or so minutes of digging, so not too bad at all. Here's a complete CodePen:

  See the Pen Leaflet with Custom Icons by Raymond Camden (@cfjedimaster) on CodePen.

A Sample Application

Let's demonstrate this with a (kinda) real-world scenario. For the next map, I'll call a function that returns a list of stores and whether or not they are currently open:

async function getStores() {
    return [
 { lat: 30.1, lng: -92.09, desc: '<b>Store One</b><br>Open 9-5 M-F', open:true },
 { lat: 30.3, lng: -92.06, desc: '<b>Store Two</b><br>Open 9-5 M-F', open: true },
 { lat: 30.1, lng: -91.8, desc: '<b>Store Three</b><br>Open 9-1 M-F', open:false }
 ];
}

And with the same custom markers I demonstrated above, I'll use them like so:

let stores = await getStores();
for(let store of stores) {
	let marker = greenIcon;
	if(!store.open) marker = redIcon;
	L.marker([store.lat, store.lng], {icon:marker}).addTo(map).bindPopup(store.desc);
}

It is fairly simple, and you can imagine multiple different icons in play based on the data for your locations. Here's the demo:

See the Pen Leaflet with Custom Icons by Raymond Camden (@cfjedimaster) on CodePen.

I think I said this in a previous post, but I love how easy Leaflet is, and when I do run into something that isn't quite as easy, I feel like it always provides a way to get to what I need. That's a sign of a good library!