Candlestick Chart

A candlestick chart showing open and closing prices of Apple stock from the end of 2017 until May 2018. Adapted from https://observablehq.com/@d3/candlestick-chart.

The (async () => { ... })() bit is a so-called Immediately Invoked Function Expression, which is just a way to define a function and run it immediately without having to give it a name. It is used here to contain all logic that depends on asynchronous operations like fetching datasets.