It’s easy to use D3 within Observable, but it’s not pre-loaded or specifically built-in. Any browser library published to npm can be loaded via require (for AMD) or dynamic import (for ES modules). I’ve published a bunch of notebooks with D3 but you’ll find other ones with THREE.js, Vega-Lite, Leaflet and other libraries.
import {canvas as flood} with {height} from "@mbostock/randomized-flood-fill"
i = {
let i = 0;
while (true) {
yield ++i;
}
}
To summarize, the body of a cell is typically either an expression or a block statement, akin to the body of an arrow function. If a cell starts with name = …, then it has a name and can be referenced by other cells. So, the name = part is specific to Observable, but the expression and block statement is normal JavaScript.
The import declaration is similar to a normal static ES import, but the with clause allows you to inject local definitions into the imported notebook.
e.g.
name = { foo: 1 }
name = { return { foo: 1} }
name = ({ foo: 1})