Exploring Recharts: using foreignObject
to render custom HTML
As we have already seen here, Recharts allows you to render any svg
element as a child element of a chart container and only accepts a svg
element when customizing Labels
or ticks
and other customizable elements (with the exception of Tooltip
, as Tooltip
is rendered outside the svg
chart, so it can accept regular html), but there are a lot of things that are just way easier to render with html. svg
allows this using the foreignObject
svg element and since Recharts can render any svg
elements, Recharts allows this as well. This can help you have custom labels which are not restricted to only svg elements.
See the below example:
This renders a custom label for a ReferenceLine
using svg
elements. So, we render a g
, and a rect
and a text
inside the group. We have to explicitly set the coordinates for the rect
and the text
, and we have to take care of all the alignments for the text
as well. To center the text
inside the rect
, we would need to set a width
for the rect
, then calculate the text
position, and what not.
Enter foreignObject
!
See the same example implemented using a foreignObject
.
We still have to take care of a few things, but, and this is a big BUT, we get the capability to render html elements, and style them using our usual css. No more figuring out the text alignment, as easy as setting the text-align
css property on the html element.
Cool, now that you are on onboard with the idea, let’s list out how to make it work:
- when using a
foreignObject
insidesvg
, we need to explicitly specify the namespace that the foreign object is from. In this case we do that here:<div xmlns=”http://www.w3.org/1999/xhtml" … >
- we still need to position the
foreignObject
container itself, similar to how we needed to do it forsvg
elements, but here we only need to align the container and all nested html elements would be aligned accordingly. - we need to set a width, height on the
foreignObject
container to set constraints, otherwise the children would not show up at all.
OR
- we can set
overflow: visible
onforeignObject
and let theheight
,width
be default to zero. This way the html elements can decide their ownwidth
and everything. This is much better so that the HTML elements are not constrained by thewidth
of theforeignObject
container itself. This also helps with complex positioning and alignment.
This was just an example, you can of course use foreignObject
anywhere you are customizing any Recharts elements.
References:
A list of all other posts in this series:
- Exploring Recharts: Reference Area
- Exploring Recharts: multiple ReferenceLine segments
- Exploring Recharts: using foreignObject to render custom HTML
- Exploring Recharts: What can be rendered inside a Recharts contianer ?
- Exploring Recharts: different ways of accessing data
- Exploring Recharts: Pulsating circle using ReferenceDot
- Exploring Recharts: LineChart with different colored segments for a single Line