How to Add Custom Annotation Line on Hover in Chart JS

How to add custom annotation line on hover in Chart JS

How to add a custom annotation line on hover in Chart js. An annotation line is a line usually vertical or horizontal line that highlights a specific point. Usually to indicate an important event on the chart or precisely see the exact data point value on the x-axis.

Video of how to add custom annotation line on hover in Chart JS

In Chart.js we create our own annotation line which is trigger on an hover effect. This video will show you how to make a line that is dashed / dotted at the top and a solid line once it hits the data point to bottom.

How to create a custom annotation line in Chart js

The video shows you exactly how to do it code wise. However, to understand the logic behind it. Chart.js is written in Javascript and drawn in the Canvas API. With the Canvas API we can truly draw anything on the Chart.js chartArea.

With a custom plugin we will draw the lines and get the matching coordinates on the x axis and y axis. Which is being triggered only once we hover on top of the specific data point.

For the hover triggering effect we will be using the structure similar to the tooltip and is part of the Chart.js API. As this does exactly the same as what we need. Watch the video to fully grasp the steps as this is a quite advance topic.