Custom Visual - Error in compiling the d3 example

[fxs7576]

Hello Looker Community,

I'm trying to get familiar in building custom visual, so I follow one of the examples (collapsible_tree) from Looker documentation. https://github.com/looker/custom_visualizations_v2/blob/master/src/examples/collapsible_tree/collap...

However, when I tried to compile that ts.file using tsc or yarn, I received three type errors (as shown in the image).

I tried debugging the type errors but to no avail. Would appreciate if anyone can guide me in troubleshooting this.

If this help, I use ' npm i --save-dev @types/d3' to get the d3 package, and 'tsc' to compile.