How to Get the Node Datum on Mouseover in D3 v6

Unable to Get Node Datum on Mouseover in D3 v6

In D3 v6, the event handling mechanism has undergone significant changes from previous versions. This article delves into these changes and provides solutions to a common issue encountered when trying to retrieve the node's datum during a mouseover event.

Event Handling in D3 v5 and Earlier

In D3 v5 and earlier, the event handling pattern followed this format:

selection.on("eventType", function(d, i, nodes) { .... })

Within the listener function, d represented the datum of the triggering element, i was its index, and nodes was the current group of elements. Additionally, event information could be accessed with d3.event.

Event Handling in D3 v6

In D3 v6, the event handling pattern has been modified as follows:

selection.on("eventType", function(event, d) { .... })

Here, the event gets passed as the first parameter to the listener directly, and the datum becomes the second parameter. As a result, d3.event has been removed.

Getting the Node Datum

To retrieve the node's datum in D3 v6, you can use the new event handling pattern. The following example demonstrates how to handle the mouseover event and access the datum:

node.on("mouseover", function(event, d) {
  console.log(d.id); // Outputs the id of the node
});

Positioning and Other Event Properties

For accessing the x, y position of the triggering event, use d3.pointer(event) instead of d3.mouse(this). To get the x and y properties, use event.x and event.y instead of d3.event.x and d3.event.y.

Summary

The key changes in event handling in D3 v6 involve passing the event as the first parameter and using event.currentTarget instead of d3.select(this). Additionally, d3.pointer(event) replaces d3.mouse(this) for positioning purposes. Understanding these changes will enable you to effectively handle events in your D3 v6 applications.

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