heatmap.js is a JavaScript library that can be used to generate web heatmaps with the html5 canvas element based on your data. Heatmap instances contain a store in order to colorize the heatmap based on relative data, which means if you're adding only a single datapoint to the store it will be displayed as the hottest (red) spot, then adding another point with a higher count, it will dynamically recalculate. The heatmaps are fully customizable - you're welcome to choose your own color gradient, change its opacity, datapoint radius and many more.